From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Fri, 19 Apr 2024 02:47:55 +0200
Subject: Adding upstream version 124.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../presentation-markup/scripts/cramped-001.html   | 627 +++++++++++++++++++++
 .../scripts/empty-underover.html                   |  68 +++
 .../scripts/mover-accent-dynamic-change-ref.html   |   9 +
 .../scripts/mover-accent-dynamic-change.html       |  16 +
 .../scripts/mprescripts-001-ref.html               |  19 +
 .../scripts/mprescripts-001.html                   |  26 +
 .../presentation-markup/scripts/none-001-ref.html  |  19 +
 .../presentation-markup/scripts/none-001.html      |  26 +
 .../presentation-markup/scripts/none-002-ref.html  |  73 +++
 .../presentation-markup/scripts/none-002.html      |  76 +++
 .../scripts/stretchy-mover-1-ref.html              |  36 ++
 .../scripts/stretchy-mover-1a.html                 |  44 ++
 .../scripts/stretchy-mover-1b.html                 |  44 ++
 .../scripts/stretchy-mover-2-ref.html              |  32 ++
 .../scripts/stretchy-mover-2a.html                 |  36 ++
 .../scripts/stretchy-mover-2b.html                 |  36 ++
 .../scripts/stretchy-mover-3-ref.html              |  28 +
 .../scripts/stretchy-mover-3.html                  |  30 +
 .../scripts/stretchy-msup-1-ref.html               |  28 +
 .../scripts/stretchy-msup-1a.html                  |  30 +
 .../scripts/stretchy-msup-1b.html                  |  32 ++
 .../scripts/stretchy-msup-1c.html                  |  34 ++
 .../scripts/stretchy-msup-1d.html                  |  33 ++
 .../scripts/stretchy-munderover-1-ref.html         |  31 +
 .../scripts/stretchy-munderover-1a.html            |  33 ++
 .../scripts/stretchy-munderover-1b.html            |  35 ++
 .../scripts/stretchy-munderover-1c.html            |  31 +
 .../scripts/stretchy-munderover-1d.html            |  34 ++
 .../scripts/stretchy-munderover-1e.html            |  34 ++
 .../scripts/stretchy-munderover-2-ref.html         |  34 ++
 .../scripts/stretchy-munderover-2a.html            |  36 ++
 .../scripts/stretchy-munderover-2b.html            |  38 ++
 .../scripts/stretchy-munderover-2c.html            |  34 ++
 .../scripts/stretchy-munderover-2d.html            |  36 ++
 .../scripts/stretchy-munderover-2e.html            |  36 ++
 .../scripts/stretchy-munderover-2f.html            |  38 ++
 .../scripts/stretchy-munderover-2g.html            |  37 ++
 .../scripts/stretchy-munderover-3-ref.html         |  31 +
 .../scripts/stretchy-munderover-3a.html            |  33 ++
 .../scripts/stretchy-munderover-3b.html            |  31 +
 .../scripts/stretchy-munderover-3c.html            |  34 ++
 .../scripts/stretchy-munderover-3d.html            |  31 +
 .../scripts/sub-vs-sup-mozilla-345563-ref.xhtml    |  22 +
 .../scripts/sub-vs-sup-mozilla-345563.xhtml        |  25 +
 .../presentation-markup/scripts/subsup-1.html      | 114 ++++
 .../presentation-markup/scripts/subsup-2.html      | 173 ++++++
 .../presentation-markup/scripts/subsup-3.html      | 192 +++++++
 .../presentation-markup/scripts/subsup-4.html      | 129 +++++
 .../presentation-markup/scripts/subsup-5.html      |  97 ++++
 .../presentation-markup/scripts/subsup-6.html      | 120 ++++
 ...y-scriptshift-attributes-001.tentative-ref.html |  35 ++
 ...egacy-scriptshift-attributes-001.tentative.html |  48 ++
 .../scripts/subsup-parameters-1.html               | 354 ++++++++++++
 .../scripts/subsup-parameters-2.html               | 181 ++++++
 .../presentation-markup/scripts/underover-1.html   | 175 ++++++
 .../underover-legacy-align-attribute-001-ref.html  |  61 ++
 .../underover-legacy-align-attribute-001.html      |  72 +++
 .../scripts/underover-parameters-1.html            | 151 +++++
 .../scripts/underover-parameters-2.html            | 151 +++++
 .../scripts/underover-parameters-3.html            | 452 +++++++++++++++
 .../scripts/underover-parameters-4.tentative.html  | 335 +++++++++++
 ...over-parameters-and-embellished-operator-1.html | 151 +++++
 ...over-parameters-and-embellished-operator-2.html | 151 +++++
 .../scripts/underover-stretchy-001-ref.html        | 167 ++++++
 .../scripts/underover-stretchy-001.html            | 270 +++++++++
 .../scripts/underover-stretchy-002-ref.html        | 167 ++++++
 .../scripts/underover-stretchy-002.html            | 272 +++++++++
 .../scripts/underover-stretchy-003-ref.html        | 167 ++++++
 .../scripts/underover-stretchy-003.html            | 272 +++++++++
 69 files changed, 6553 insertions(+)
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/cramped-001.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/empty-underover.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/none-001-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/none-001.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/none-002-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/none-002.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1c.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1d.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1c.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1d.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1e.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2c.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2d.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2e.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2f.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2g.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3a.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3b.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3c.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3d.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563-ref.xhtml
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563.xhtml
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-1.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-2.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-3.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-4.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-5.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-6.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-1.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-2.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-1.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-1.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-2.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-3.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-4.tentative.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-1.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-2.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003-ref.html
 create mode 100644 testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003.html

(limited to 'testing/web-platform/tests/mathml/presentation-markup/scripts')

diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/cramped-001.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/cramped-001.html
new file mode 100644
index 0000000000..e03b4d968d
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/cramped-001.html
@@ -0,0 +1,627 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Cramped elements</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<link rel="help" href="https://w3c.github.io/mathml-core/#fractions-mfrac">
+<link rel="help" href="https://w3c.github.io/mathml-core/#radicals-msqrt-mroot">
+<link rel="help" href="https://w3c.github.io/mathml-core/#displaystyle-and-scriptlevel-in-scripts">
+<link rel="help" href="https://w3c.github.io/mathml-core/#user-agent-stylesheet">
+<meta name="assert" content="Verify default calculation of math-shift on MathML elements">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<script src="/mathml/support/box-navigation.js"></script>
+<style>
+  math {
+      font-family: superscriptshiftupcramped5000;
+  }
+  math, math * {
+      font-size: 10px;
+      background: lightyellow;
+  }
+  @font-face {
+    font-family: superscriptshiftupcramped5000;
+    src: url("/fonts/math/scripts-superscriptshiftupcramped5000.woff");
+  }
+  .testedElement *:first-child {
+      background: lightblue;
+  }
+  .testedElement *:last-child {
+      background: pink;
+  }
+</style>
+<script>
+  function assert_cramped(id, expected, name) {
+      const emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+      const superscriptshiftupcramped = 5000 * emToPx;
+      var container = document.getElementById(id);
+      var msup = container.getElementsByClassName("testedElement")[0];
+      var base = firstInFlowChild(msup);
+      var script = nextInFlowSibling(base);
+      var shift = base.getBoundingClientRect().bottom - script.getBoundingClientRect().bottom;
+      if (expected)
+          assert_greater_than(shift, superscriptshiftupcramped / 2, `${name || id} should be cramped`);
+      else
+          assert_less_than(shift, superscriptshiftupcramped / 2, `${name || id} should not be cramped`);
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("math-001", false);
+          assert_cramped("mrow-001", false, "mrow");
+      }, "child of non-cramped element");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mrow-002", true);
+      }, "child of cramped element");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("msqrt-001", true);
+      }, "child of msqrt");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mroot-001", true);
+      }, "child of mroot");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mfrac-001", false, "numerator");
+          assert_cramped("mfrac-002", true, "denominator");
+      }, "child of mfrac");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("msub-001", false, "base");
+          assert_cramped("msub-002", true, "subscript");
+      }, "child of msub");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("msup-001", false, "base");
+          assert_cramped("msup-002", false, "superscript");
+      }, "child of msup");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("msubsup-001", false, "base");
+          assert_cramped("msubsup-002", true, "subscript");
+          assert_cramped("msubsup-003", false, "superscript");
+      }, "child of msubsup");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("munder-001", false, "base");
+          assert_cramped("munder-002", false, "underscript");
+      }, "child of munder");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mover-001", false, "base");
+          assert_cramped("mover-002", false, "overscript");
+      }, "child of mover (non-accent overscript)");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("munderover-001", false, "base");
+          assert_cramped("munderover-002", false, "underscript");
+          assert_cramped("munderover-003", false, "overscript");
+      }, "child of munderover (non-accent overscript)");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mover-003", true, "base");
+          assert_cramped("mover-004", false, "overscript");
+      }, "accent child of mover (accent overscript)");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("munderover-004", true, "base");
+          assert_cramped("munderover-005", false, "underscript");
+          assert_cramped("munderover-006", false, "overscript");
+      }, "accent child of munderover (accent overscript)");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("mmultiscripts-001", false, "base");
+          assert_cramped("mmultiscripts-002", true, "post-subscript");
+          assert_cramped("mmultiscripts-003", false, "post-superscript");
+          assert_cramped("mmultiscripts-004", true, "pre-subscript");
+          assert_cramped("mmultiscripts-005", false, "post-superscript");
+      }, "mmultiscripts");
+
+      test(function() {
+          assert_true(MathMLFeatureDetection.has_mspace());
+          assert_cramped("css-001", false);
+          assert_cramped("css-002", true);
+          assert_cramped("css-003", true);
+          assert_cramped("css-004", false);
+      }, "element with specified CSS math-style");
+
+      done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math id="math-001">
+      <msup class="testedElement">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math>
+      <mrow id="mrow-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </mrow>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msqrt>
+        <!-- This is a child of a msqrt so it is cramped. As a consequence,
+             all its descendants are cramped too. -->
+        <munderover>
+          <mover>
+            <munder>
+              <msubsup>
+                <msup>
+                  <msub>
+                    <mfrac>
+                      <mrow id="mrow-002">
+                        <msup class="testedElement">
+                          <mspace height="2em" width="2em"/>
+                          <mspace height="1em" width="1em"/>
+                        </msup>
+                      </mrow>
+                      <mspace/>
+                    </mfrac>
+                    <mspace/>
+                  </msub>
+                  <mspace/>
+                </msup>
+                <mspace/>
+                <mspace/>
+              </msubsup>
+              <mspace/>
+            </munder>
+            <mspace/>
+          </mover>
+          <mspace/>
+          <mspace/>
+        </munderover>
+      </msqrt>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msqrt id="msqrt-001">
+        <mn>0</mn>
+        <mn>1</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>3</mn>
+        <mn>4</mn>
+      </msqrt>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mroot id="mroot-001">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </mroot>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mroot id="mroot-002">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </mroot>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mfrac id="mfrac-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </mfrac>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mfrac id="mfrac-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </mfrac>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msub id="msub-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </msub>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msub id="msub-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </msub>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msup id="msup-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </msup>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msup id="msup-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </msup>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msubsup id="msubsup-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+        <mn>2</mn>
+      </msubsup>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msubsup id="msubsup-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>2</mn>
+      </msubsup>
+    </math>
+  </p>
+  <p>
+    <math>
+      <msubsup id="msubsup-003">
+        <mn>0</mn>
+        <mn>1</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </msubsup>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munder id="munder-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </munder>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munder id="munder-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </munder>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mover id="mover-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </mover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mover id="mover-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </mover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mover accent="true" id="mover-003">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+      </mover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mover accent="true" id="mover-004">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </mover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover id="munderover-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+        <mn>2</mn>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover id="munderover-002">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>2</mn>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover id="munderover-003">
+        <mn>0</mn>
+        <mn>1</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover accent="true" id="munderover-004">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+        <mn>2</mn>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover accent="true" id="munderover-005">
+        <mn>0</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>2</mn>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <munderover accent="true" id="munderover-006">
+        <mn>0</mn>
+        <mn>1</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+      </munderover>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts id="mmultiscripts-001">
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>1</mn>
+        <mn>2</mn>
+        <mn>3</mn>
+        <mn>4</mn>
+        <mn>5</mn>
+        <mn>6</mn>
+        <mprescripts/>
+        <mn>7</mn>
+        <mn>8</mn>
+        <mn>9</mn>
+        <mn>10</mn>
+        <mn>11</mn>
+        <mn>12</mn>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts id="mmultiscripts-002">
+        <mn>0</mn>
+        <mn>1</mn>
+        <mn>2</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>4</mn>
+        <mn>5</mn>
+        <mn>6</mn>
+        <mprescripts/>
+        <mn>7</mn>
+        <mn>8</mn>
+        <mn>9</mn>
+        <mn>10</mn>
+        <mn>11</mn>
+        <mn>12</mn>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts id="mmultiscripts-003">
+        <mn>0</mn>
+        <mn>1</mn>
+        <mn>2</mn>
+        <mn>3</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>5</mn>
+        <mn>6</mn>
+        <mprescripts/>
+        <mn>7</mn>
+        <mn>8</mn>
+        <mn>9</mn>
+        <mn>10</mn>
+        <mn>11</mn>
+        <mn>12</mn>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts id="mmultiscripts-004">
+        <mn>0</mn>
+        <mn>1</mn>
+        <mn>2</mn>
+        <mn>3</mn>
+        <mn>4</mn>
+        <mn>5</mn>
+        <mn>6</mn>
+        <mprescripts/>
+        <mn>7</mn>
+        <mn>8</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>10</mn>
+        <mn>11</mn>
+        <mn>12</mn>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts id="mmultiscripts-005">
+        <mn>0</mn>
+        <mn>1</mn>
+        <mn>2</mn>
+        <mn>3</mn>
+        <mn>4</mn>
+        <mn>5</mn>
+        <mn>6</mn>
+        <mprescripts/>
+        <mn>7</mn>
+        <mn>8</mn>
+        <mn>9</mn>
+        <msup class="testedElement">
+          <mspace height="2em" width="2em"/>
+          <mspace height="1em" width="1em"/>
+        </msup>
+        <mn>11</mn>
+        <mn>12</mn>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math id="css-001" style="math-shift: normal">
+      <msup class="testedElement">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-002" style="math-shift: compact">
+      <msup class="testedElement">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-003" style="math-shift: normal">
+      <msup class="testedElement" style="math-shift: compact">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+    <math id="css-004" style="math-shift: compact">
+      <msup class="testedElement" style="math-shift: normal">
+        <mspace height="2em" width="2em"/>
+        <mspace height="1em" width="1em"/>
+      </msup>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/empty-underover.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/empty-underover.html
new file mode 100644
index 0000000000..b5fcc9c4ca
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/empty-underover.html
@@ -0,0 +1,68 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Test Script and Limit Schemata</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#script-and-limit-schemata">
+<meta name="assert" content="Script and Limit Schemata should not render anything when empty.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<script>
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      ["over", "under", "underover", "sub", "sup", "subsup", "multiscripts"].forEach(function(name) {
+        assert_true(MathMLFeatureDetection.has_mspace());
+        assert_approx_equals(getBox(name).width, 0, epsilon, "width of empty " + name);
+        assert_approx_equals(getBox(name).height, 0, epsilon, "height of empty " + name);
+      });
+    }, "Size of empty script elements");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math>
+        <munderover id="underover">
+        </munderover>
+      </math>
+      <math>
+        <munder id="under">
+        </munder>
+      </math>
+      <math>
+        <mover id="over">
+        </mover>
+      </math>
+      <math>
+        <msub id="sub">
+        </msub>
+      </math>
+      <math>
+        <msup id="sup">
+        </msup>
+      </math>
+      <math>
+        <msubsup id="subsup">
+        </msubsup>
+      </math>
+      <math>
+        <mmultiscripts id="multiscripts">
+        </mmultiscripts>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change-ref.html
new file mode 100644
index 0000000000..a4f16aa07f
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change-ref.html
@@ -0,0 +1,9 @@
+<!doctype html>
+<title>MathML Reference</title>
+<p>The 1's below should have the same size</p>
+<math>
+  <mover accent="true">
+    <mn>1</mn>
+    <mn>1</mn>
+  </mover>
+</math>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change.html
new file mode 100644
index 0000000000..a744149e60
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/mover-accent-dynamic-change.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<title>MathML: Dynamically change accent on mover</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#displaystyle-and-scriptlevel-in-scripts">
+<link rel="match" href="mover-accent-dynamic-change-ref.html">
+<meta name="assert" content="Test that setting the accent attribute on mover takes effect">
+<p>The 1's below should have the same size</p>
+<math>
+  <mover id="m">
+    <mn>1</mn>
+    <mn>1</mn>
+  </mover>
+</math>
+<script>
+  document.body.offsetTop;
+  m.setAttribute("accent", "true");
+</script>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001-ref.html
new file mode 100644
index 0000000000..f8631539c0
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001-ref.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>mprescripts should render as an mrow (reference)</title>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <mspace width="10px" height="20px" style="background: cyan;"></mspace>
+        <mspace width="30px" height="10px" depth="5px" style="background: blue;"></mspace>
+        <mspace width="20px" height="15px" depth="30px" style="background: lightblue;"></mspace>
+        <mspace width="25px" depth="20px" style="background: cyan;"></mspace>
+        <mspace width="40px" height="5px" depth="15px" style="background: blue;"></mspace>
+        <mspace width="20px" height="35px" depth="5px" style="background: lightblue;"></mspace>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001.html
new file mode 100644
index 0000000000..2435b6291d
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/mprescripts-001.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>mprescripts should render as an mrow</title>
+    <link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+    <meta name="assert" content="Verify that mprescripts uses mrow layout">
+    <link rel="match" href="mprescripts-001-ref.html">
+  </head>
+  <body>
+    <math>
+      <mprescripts>
+        <mspace width="10px" height="20px" style="background: cyan;"></mspace>
+        <mspace width="30px" height="10px" depth="5px" style="background: blue;"></mspace>
+        <mspace width="20px" height="15px" depth="30px" style="background: lightblue;"></mspace>
+        <mspace width="25px" depth="20px" style="background: cyan;"></mspace>
+        <mspace width="40px" height="5px" depth="15px" style="background: blue;"></mspace>
+        <mspace width="20px" height="35px" depth="5px" style="background: lightblue;"></mspace>
+      </mprescripts>
+    </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>
+      MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    </script>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001-ref.html
new file mode 100644
index 0000000000..55add01415
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001-ref.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>none should render as an mrow (reference)</title>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <mspace width="10px" height="20px" style="background: cyan;"></mspace>
+        <mspace width="30px" height="10px" depth="5px" style="background: blue;"></mspace>
+        <mspace width="20px" height="15px" depth="30px" style="background: lightblue;"></mspace>
+        <mspace width="25px" depth="20px" style="background: cyan;"></mspace>
+        <mspace width="40px" height="5px" depth="15px" style="background: blue;"></mspace>
+        <mspace width="20px" height="35px" depth="5px" style="background: lightblue;"></mspace>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001.html
new file mode 100644
index 0000000000..f1bfb442f7
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-001.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>none should render as an mrow</title>
+    <link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+    <meta name="assert" content="Verify that none uses mrow layout">
+    <link rel="match" href="none-001-ref.html">
+  </head>
+  <body>
+    <math>
+      <none>
+        <mspace width="10px" height="20px" style="background: cyan;"></mspace>
+        <mspace width="30px" height="10px" depth="5px" style="background: blue;"></mspace>
+        <mspace width="20px" height="15px" depth="30px" style="background: lightblue;"></mspace>
+        <mspace width="25px" depth="20px" style="background: cyan;"></mspace>
+        <mspace width="40px" height="5px" depth="15px" style="background: blue;"></mspace>
+        <mspace width="20px" height="35px" depth="5px" style="background: lightblue;"></mspace>
+      </none>
+    </math>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>
+      MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    </script>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002-ref.html
new file mode 100644
index 0000000000..dac4dab553
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002-ref.html
@@ -0,0 +1,73 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>none used at other places than mmultiscripts' script (reference)</title>
+    <link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+    <style>
+      math { font: 25px/1 Ahem; }
+    </style>
+  </head>
+  <body>
+    <p>
+      <math>
+        <msub>
+          <mrow></mrow>
+          <mn>2</mn>
+        </msub>
+      </math>
+      <math>
+        <msub>
+          <mn>1</mn>
+          <mrow></mrow>
+        </msub>
+      </math>
+    </p>
+    <p>
+      <math>
+        <msup>
+          <mrow></mrow>
+          <mn>2</mn>
+        </msup>
+      </math>
+      <math>
+        <msup>
+          <mn>1</mn>
+          <mrow></mrow>
+        </msup>
+      </math>
+    </p>
+    <p>
+      <math>
+        <msubsup>
+          <mrow></mrow>
+          <mn>2</mn>
+          <mn>3</mn>
+        </msubsup>
+      </math>
+      <math>
+        <msubsup>
+          <mn>1</mn>
+          <mrow></mrow>
+          <mn>3</mn>
+        </msubsup>
+      </math>
+      <math>
+        <msubsup>
+          <mn>1</mn>
+          <mn>2</mn>
+          <mrow></mrow>
+        </msubsup>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mmultiscripts>
+          <mrow></mrow>
+          <mn>2</mn>
+          <mn>3</mn>
+        </mmultiscripts>
+      </math>
+    </p>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002.html
new file mode 100644
index 0000000000..d1f3a3a0e1
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/none-002.html
@@ -0,0 +1,76 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>none used at other places than mmultiscripts' script</title>
+    <link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+    <meta name="assert" content="none can be used at other places than mmultiscripts' script, without triggering 'invalid markup'">
+    <link rel="match" href="none-002-ref.html">
+    <link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+    <style>
+      math { font: 25px/1 Ahem; }
+    </style>
+  </head>
+  <body>
+    <p>
+      <math>
+        <msub>
+          <none/>
+          <mn>2</mn>
+        </msub>
+      </math>
+      <math>
+        <msub>
+          <mn>1</mn>
+          <none/>
+        </msub>
+      </math>
+    </p>
+    <p>
+      <math>
+        <msup>
+          <none/>
+          <mn>2</mn>
+        </msup>
+      </math>
+      <math>
+        <msup>
+          <mn>1</mn>
+          <none/>
+        </msup>
+      </math>
+    </p>
+    <p>
+      <math>
+        <msubsup>
+          <none/>
+          <mn>2</mn>
+          <mn>3</mn>
+        </msubsup>
+      </math>
+      <math>
+        <msubsup>
+          <mn>1</mn>
+          <none/>
+          <mn>3</mn>
+        </msubsup>
+      </math>
+      <math>
+        <msubsup>
+          <mn>1</mn>
+          <mn>2</mn>
+          <none/>
+        </msubsup>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mmultiscripts>
+          <none/>
+          <mn>2</mn>
+          <mn>3</mn>
+        </mmultiscripts>
+      </math>
+    </p>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1-ref.html
new file mode 100644
index 0000000000..96cba038a4
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1-ref.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+      #container {
+        width: 800px;
+        height: 600px;
+        overflow: hidden;
+        background: lightblue;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="container">
+      <math display=block>
+        <mover>
+          <mo stretchy="true">&#x2192;</mo>
+          <mn>BBBBBBBBB</mn>
+        </mover>
+      </math>
+    </div>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1a.html
new file mode 100644
index 0000000000..8a87c2387f
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1a.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-mover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+      #container {
+        width: 800px;
+        height: 600px;
+        overflow: hidden;
+        background: lightblue;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="container">
+      <math display=block>
+        <mrow>
+          <mspace width="10em"/>
+          <mrow>
+            <mover>
+              <mo stretchy="true">&#x2192;</mo>
+              <mn>BBBBBBBBB</mn>
+            </mover>
+          </mrow>
+          <mspace width="10em"/>
+        </mrow>
+      </math>
+    </div>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1b.html
new file mode 100644
index 0000000000..da35123513
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-1b.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-mover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+      #container {
+        width: 800px;
+        height: 600px;
+        overflow: hidden;
+        background: lightblue;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="container">
+      <math display=block>
+        <mrow>
+          <mspace depth="50em"/>
+          <mrow>
+            <mover>
+              <mo stretchy="true">&#x2192;</mo>
+              <mn>BBBBBBBBB</mn>
+            </mover>
+          </mrow>
+          <mspace depth="50em"/>
+        </mrow>
+      </math>
+    </div>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2-ref.html
new file mode 100644
index 0000000000..e9b24785d3
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2-ref.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math display=block>
+     <mrow>
+      <mrow>
+        <mover>
+          <mo stretchy="false">&#x2191;</mo>
+          <mn>B</mn>
+        </mover>
+      </mrow>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2a.html
new file mode 100644
index 0000000000..87738363cd
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2a.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-mover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math display=block>
+     <mrow>
+     <mspace width="10em"/>
+      <mrow>
+        <mover>
+          <mo stretchy="true">&#x2191;</mo>
+          <mn>B</mn>
+        </mover>
+      </mrow>
+      <mspace width="10em"/>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2b.html
new file mode 100644
index 0000000000..6f44ffe17d
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-2b.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="mismatch" href="stretchy-mover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math display=block>
+     <mrow>
+     <mspace depth="5em"/>
+      <mrow>
+        <mover>
+          <mo stretchy="true">&#x2191;</mo>
+          <mn>B</mn>
+        </mover>
+      </mrow>
+      <mspace depth="5em"/>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3-ref.html
new file mode 100644
index 0000000000..10e0779b98
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3-ref.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mover>
+        <mo stretchy="false">&Vert;</mo>
+        <mn>BBBBBBBBB</mn>
+      </mover>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3.html
new file mode 100644
index 0000000000..9becf31d14
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-mover-3.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy mover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-mover-3-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mover>
+        <mo stretchy="true">&Vert;</mo>
+        <mn>BBBBBBBBB</mn>
+      </mover>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1-ref.html
new file mode 100644
index 0000000000..7b6b6d72ad
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1-ref.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Non-stretchy msup</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <msup>
+        <mo stretchy="false">&#x2192;</mo>
+        <mtext>AAAAAA</mtext>
+      </msup>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1a.html
new file mode 100644
index 0000000000..1abf64aad6
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1a.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Non-stretchy msup</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-msup-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <msup>
+        <mo stretchy="true">&#x2192;</mo>
+        <mtext>AAAAAA</mtext>
+      </msup>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1b.html
new file mode 100644
index 0000000000..c6e0a8aaab
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1b.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Non-stretchy msup</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-msup-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <mrow>
+        <msup>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+        </msup>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1c.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1c.html
new file mode 100644
index 0000000000..056000566a
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1c.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Non-stretchy msup</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-msup-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <mrow>
+        <mrow>
+          <msup>
+            <mo stretchy="true">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+          </msup>
+        </mrow>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1d.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1d.html
new file mode 100644
index 0000000000..a1ac5772f2
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-msup-1d.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Non-stretchy msup</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-msup-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <mrow>
+        <msup>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+        </msup>
+        <mspace width="5em" />
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1-ref.html
new file mode 100644
index 0000000000..587d37163d
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1-ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+</head>
+  <body>
+    <math >
+      <mrow>
+        <munderover>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1a.html
new file mode 100644
index 0000000000..0dfd5ad40b
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1a.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="mismatch" href="stretchy-munderover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mo stretchy="false">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1b.html
new file mode 100644
index 0000000000..f4a2c67c58
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1b.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <mrow>
+         <munderover>
+            <mo stretchy="true">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+        </mrow>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1c.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1c.html
new file mode 100644
index 0000000000..6430545794
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1c.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <munderover>
+        <mo stretchy="true">&#x2192;</mo>
+        <mtext>AAAAAA</mtext>
+        <mtext>BBBBBB</mtext>
+        </munderover>
+      </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1d.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1d.html
new file mode 100644
index 0000000000..d2345c5f14
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1d.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+          <mtext>BBBBBB</mtext>
+          </munderover>
+        <mspace width="5em" />
+        </mrow>
+      </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1e.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1e.html
new file mode 100644
index 0000000000..ba959a5879
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-1e.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-1-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mo stretchy="true" lspace="0em" rspace="0em">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+          <mtext>BBBBBB</mtext>
+          </munderover>
+        <mn></mn>
+        </mrow>
+      </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2-ref.html
new file mode 100644
index 0000000000..f43f659240
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2-ref.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math >
+      <mrow>
+        <msup>
+          <munderover>
+            <mo stretchy="true">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+          <mtext>CCCCCC</mtext>
+        </msup>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2a.html
new file mode 100644
index 0000000000..54aea8d7c9
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2a.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="mismatch" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <msup>
+          <munderover>
+            <mo stretchy="false">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+          <mtext>CCCCCC</mtext>
+        </msup>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2b.html
new file mode 100644
index 0000000000..6420f01dd7
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2b.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <mrow>
+          <msup>
+            <munderover>
+              <mo stretchy="true">&#x2192;</mo>
+              <mtext>AAAAAA</mtext>
+              <mtext>BBBBBB</mtext>
+            </munderover>
+            <mtext>CCCCCC</mtext>
+          </msup>
+        </mrow>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2c.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2c.html
new file mode 100644
index 0000000000..3a77e78078
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2c.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <msup>
+        <munderover>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>AAAAAA</mtext>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+        <mtext>CCCCCC</mtext>
+      </msup>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2d.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2d.html
new file mode 100644
index 0000000000..30a7ca2e72
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2d.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <msup>
+          <munderover>
+            <mo stretchy="true">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+          <mtext>CCCCCC</mtext>
+        </msup>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2e.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2e.html
new file mode 100644
index 0000000000..199c101b6a
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2e.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <msup>
+        <mrow>
+          <munderover>
+            <mo stretchy="true">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+        </mrow>
+        <mtext>CCCCCC</mtext>
+      </msup>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2f.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2f.html
new file mode 100644
index 0000000000..5b736fda0a
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2f.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <msup>
+        <mrow>
+          <mrow>
+            <munderover>
+              <mo stretchy="true">&#x2192;</mo>
+              <mtext>AAAAAA</mtext>
+              <mtext>BBBBBB</mtext>
+            </munderover>
+          </mrow>
+        </mrow>
+        <mtext>CCCCCC</mtext>
+      </msup>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2g.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2g.html
new file mode 100644
index 0000000000..11cca42de1
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-2g.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-2-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <msup>
+          <munderover>
+            <mo stretchy="true" lspace="0em" rspace="0em">&#x2192;</mo>
+            <mtext>AAAAAA</mtext>
+            <mtext>BBBBBB</mtext>
+          </munderover>
+          <mtext>CCCCCC</mtext>
+        </msup>
+        <mn></mn>
+        </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3-ref.html
new file mode 100644
index 0000000000..67b3492ec8
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3-ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mtext>AAAAAA</mtext>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+      </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3a.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3a.html
new file mode 100644
index 0000000000..dd41c82def
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3a.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="mismatch" href="stretchy-munderover-3-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mtext>AAAAAA</mtext>
+          <mo stretchy="false">&#x2192;</mo>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+     </mrow>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3b.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3b.html
new file mode 100644
index 0000000000..b4619bfef9
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3b.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-3-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <munderover>
+        <mtext>AAAAAA</mtext>
+        <mo stretchy="true">&#x2192;</mo>
+        <mtext>BBBBBB</mtext>
+        </munderover>
+      </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3c.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3c.html
new file mode 100644
index 0000000000..004349f831
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3c.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="match" href="stretchy-munderover-3-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <mrow>
+        <munderover>
+          <mtext>AAAAAA</mtext>
+          <mo stretchy="true">&#x2192;</mo>
+          <mtext>BBBBBB</mtext>
+        </munderover>
+        <mspace width="5em" />
+        </mrow>
+      </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3d.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3d.html
new file mode 100644
index 0000000000..e5cf01f23e
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/stretchy-munderover-3d.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Stretchy munderover</title>
+    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
+    <link rel="mismatch" href="stretchy-munderover-3-ref.html"/>
+    <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=687807"/>
+    <link rel="stylesheet" href="/fonts/ahem.css" />
+    <style>
+      @font-face {
+        font-family: operators;
+        src: url("/fonts/math/operators.woff");
+      }
+      math {
+        font: 25px/1 Ahem;
+      }
+      mo {
+        font-family: operators;
+      }
+    </style>
+  </head>
+  <body>
+    <math>
+      <munderover>
+        <mtext>AAAAAA</mtext>
+        <mo stretchy="false">&#x2192;</mo>
+        <mtext>BBBBBB</mtext>
+      </munderover>
+    </math>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563-ref.xhtml b/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563-ref.xhtml
new file mode 100644
index 0000000000..dc57aa3506
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563-ref.xhtml
@@ -0,0 +1,22 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0//EN" "http://www.w3.org/Math/DTD/mathml2/xhtml-math11-f.dtd" >
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+
+<head>
+
+</head>
+
+<body>
+
+<p>
+  <math xmlns="http://www.w3.org/1998/Math/MathML">
+    <msup>
+      <mi>x</mi>
+      <mn>2</mn>
+    </msup>
+  </math>
+</p>
+
+</body>
+
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563.xhtml b/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563.xhtml
new file mode 100644
index 0000000000..5c8d78952f
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/sub-vs-sup-mozilla-345563.xhtml
@@ -0,0 +1,25 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0//EN" "http://www.w3.org/Math/DTD/mathml2/xhtml-math11-f.dtd" >
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+
+<head>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup"/>
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=345563"/>
+<link rel="mismatch" href="sub-vs-sup-mozilla-345563-ref.xhtml"/>
+<meta name="assert" content="Subscript should not render the same as superscript."/>
+</head>
+
+<body>
+
+<p>
+  <math xmlns="http://www.w3.org/1998/Math/MathML">
+    <msub>
+      <mi>x</mi>
+      <mn>2</mn>
+    </msub>
+  </math>
+</p>
+
+</body>
+
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-1.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-1.html
new file mode 100644
index 0000000000..1117e1008e
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-1.html
@@ -0,0 +1,114 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts metrics</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Basic metrics for elements msub, msup and msubsup.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  math, mspace {
+    font: 25px/1 Ahem;
+  }
+</style>
+<script>
+  /* This test does not use a font with a MATH table and does not verify layout
+     rules in a very strict way. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      assert_less_than_equal(getBox("msubBase").right, getBox("msubSub").left, e, "msub: subscript is after base");
+      assert_less_than_equal(getBox("msupBase").right, getBox("msupSup").left, e, "msup: superscript is after base");
+      assert_less_than_equal(getBox("msubsupBase").right, getBox("msubsupSub").left, e, "msubsup: subscript is after base");
+      assert_less_than_equal(getBox("msubsupBase").right, getBox("msubsupSup").left, e, "msubsup: superscript is after base");
+
+      e = 3;
+      assert_approx_equals(getBox("msubBase").right, getBox("msubSub").left, e, "msub: space between base and subscript is small");
+      assert_approx_equals(getBox("msubBase").right, getBox("msubSub").left, e, "msub: subscript is after base");
+      assert_approx_equals(getBox("msupBase").right, getBox("msupSup").left, e, "msup: superscript is after base");
+      assert_approx_equals(getBox("msubsupBase").right, getBox("msubsupSub").left, e, "msubsup: subscript is after base");
+      assert_approx_equals(getBox("msubsupBase").right, getBox("msubsupSup").left, e, "msubsup: superscript is after base");
+    }, "Respective horizontal positions");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      assert_approx_equals(getBox("msubBase").middle, getBox("baseline").bottom, e, "msub: base is placed on the baseline");
+      assert_approx_equals(getBox("msupBase").middle, getBox("baseline").bottom, e, "msup: base is placed on the baseline");
+      assert_approx_equals(getBox("msubsupBase").middle, getBox("baseline").bottom, e, "msubsup: base is placed on the baseline");
+    }, "Alignment of the base on the baseline");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      assert_greater_than(getBox("msubSub").middle, getBox("msubBase").middle, "msub: script is placed at the bottom of the base");
+      assert_less_than(getBox("msupSup").middle, getBox("msupBase").middle, "msup: script is placed at the top of the base");
+      assert_greater_than(getBox("msubsupSub").middle, getBox("msubsupBase").middle, "msubsup: script is placed at the bottom of the base");
+      assert_less_than(getBox("msubsupSup").middle, getBox("msubsupBase").middle, "msubsup: script is placed at the top of the base");
+    }, "Vertical position of scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 5;
+      assert_approx_equals(getBox("msub").width, getBox("msubSub").right - getBox("msubBase").left, e, "msub: width is determined by the left/right sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("msup").width, getBox("msupSup").right - getBox("msupBase").left, e, "msup: width is determined by the left/right sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("msubsup").width, Math.max(getBox("msubsupSub").right, getBox("msubsupSup").right) - getBox("msubsupBase").left, e, "msubsup: width is determined by the left/right sides of base/scripts (+ some space after script)");
+    }, "Width of scripted elements");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      assert_greater_than_equal(getBox("msub").height, getBox("msubBase").height, e, "msub: height is at least the one of the base");
+      assert_greater_than_equal(getBox("msup").height, getBox("msupBase").height, e, "msup: height is at least the one of the base");
+      assert_greater_than_equal(getBox("msubsup").height, getBox("msubsupBase").height, e, "msubsup: height is at least the one of the base");
+
+      assert_approx_equals(getBox("msub").height, Math.max(getBox("msubSub").bottom, getBox("msubBase").bottom) - getBox("msubBase").top, e, "msub: height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("msup").height, getBox("msupBase").bottom - Math.min(getBox("msupSup").top, getBox("msupBase").top), e, "msup: height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("msubsup").height, Math.max(getBox("msubSub").bottom, getBox("msubBase").bottom) - Math.min(getBox("msupSup").top, getBox("msupBase").top), e, "msubsup: height is determined by the top/bottom sides of base/scripts");
+    }, "Height of scripted elements");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <msub id="msub" style="background: green">
+        <mspace id="msubBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubSub" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msub>
+      <msup id="msup" style="background: blue">
+        <mspace id="msupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msup>
+      <msubsup id="msubsup" style="background: green">
+        <mspace id="msubsupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubsupSub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="msubsupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msubsup>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-2.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-2.html
new file mode 100644
index 0000000000..9c89dd3727
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-2.html
@@ -0,0 +1,173 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts metrics</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Basic metrics for the mmultiscript element.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  math, mspace {
+    font: 25px/1 Ahem;
+  }
+</style>
+<script>
+  /* This test does not use a font with a MATH table and does not verify layout
+     rules in a very strict way. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      assert_less_than_equal(getBox("msubBase").right, getBox("msubSub").left, e, "subscript is after base");
+      assert_less_than_equal(getBox("msupBase").right, getBox("msupSup").left, e, "superscript is after base");
+      assert_less_than_equal(getBox("msubsupBase").right, getBox("msubsupSub").left, e, "subscript is after base");
+      assert_less_than_equal(getBox("msubsupBase").right, getBox("msubsupSup").left, e, "superscript is after base");
+
+     assert_greater_than_equal(getBox("premsubBase").right, getBox("premsubSub").left, e, "subscript is before base");
+      assert_greater_than_equal(getBox("premsupBase").right, getBox("premsupSup").left, e, "superscript is before base");
+      assert_greater_than_equal(getBox("premsubsupBase").right, getBox("premsubsupSub").left, e, "subscript is before base");
+      assert_greater_than_equal(getBox("premsubsupBase").right, getBox("premsubsupSup").left, e, "superscript is before base");
+
+      e = 3;
+      assert_approx_equals(getBox("msubBase").right, getBox("msubSub").left, e, "msub: space between base and subscript is small");
+      assert_approx_equals(getBox("msubBase").right, getBox("msubSub").left, e, "msub: subscript is after base");
+      assert_approx_equals(getBox("msupBase").right, getBox("msupSup").left, e, "msup: superscript is after base");
+      assert_approx_equals(getBox("msubsupBase").right, getBox("msubsupSub").left, e, "msubsup: subscript is after base");
+      assert_approx_equals(getBox("msubsupBase").right, getBox("msubsupSup").left, e, "msubsup: superscript is after base");
+
+      assert_approx_equals(getBox("premsubBase").left, getBox("premsubSub").right, e, "msub: space between base and subscript is small");
+      assert_approx_equals(getBox("premsubBase").left, getBox("premsubSub").right, e, "msub: subscript is after base");
+      assert_approx_equals(getBox("premsupBase").left, getBox("premsupSup").right, e, "msup: superscript is after base");
+      assert_approx_equals(getBox("premsubsupBase").left, getBox("premsubsupSub").right, e, "msubsup: subscript is after base");
+      assert_approx_equals(getBox("premsubsupBase").left, getBox("premsubsupSup").right, e, "msubsup: superscript is after base");
+    }, "Respective horizontal positions");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      assert_approx_equals(getBox("msubBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+      assert_approx_equals(getBox("msupBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+      assert_approx_equals(getBox("msubsupBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+      assert_approx_equals(getBox("premsubBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+      assert_approx_equals(getBox("premsupBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+      assert_approx_equals(getBox("premsubsupBase").middle, getBox("baseline").bottom, e, "base is placed on the baseline");
+    }, "Alignment of the base on the baseline");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      assert_greater_than(getBox("msubSub").middle, getBox("msubBase").middle, "script is placed at the bottom of the base");
+      assert_less_than(getBox("msupSup").middle, getBox("msupBase").middle, "script is placed at the top of the base");
+      assert_greater_than(getBox("msubsupSub").middle, getBox("msubsupBase").middle, "script is placed at the bottom of the base");
+      assert_less_than(getBox("msubsupSup").middle, getBox("msubsupBase").middle, "script is placed at the top of the base");
+
+      assert_greater_than(getBox("premsubSub").middle, getBox("premsubBase").middle, "script is placed at the bottom of the base");
+      assert_less_than(getBox("premsupSup").middle, getBox("premsupBase").middle, "script is placed at the top of the base");
+      assert_greater_than(getBox("premsubsupSub").middle, getBox("premsubsupBase").middle, "script is placed at the bottom of the base");
+      assert_less_than(getBox("premsubsupSup").middle, getBox("premsubsupBase").middle, "script is placed at the top of the base");
+    }, "Vertical position of scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 3;
+      assert_approx_equals(getBox("msub").width, getBox("msubSub").right - getBox("msubBase").left, e, "width is determined by the left/right sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("msup").width, getBox("msupSup").right - getBox("msupBase").left, e, "width is determined by the left/right sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("msubsup").width, Math.max(getBox("msubsupSub").right, getBox("msubsupSup").right) - getBox("msubsupBase").left, e, "width is determined by the left/right sides of base/scripts (+ some space after script)");
+
+      assert_approx_equals(getBox("premsub").width, getBox("premsubBase").right - getBox("premsubSub").left, e, "width is determined by the right/left sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("premsup").width, getBox("premsupBase").right - getBox("premsupSup").left, e, "width is determined by the right/left sides of base/script (+ some space after script)");
+      assert_approx_equals(getBox("premsubsup").width, getBox("premsubsupBase").right - Math.min(getBox("premsubsupSub").left, getBox("premsubsupSup").left), e, "width is determined by the right/left sides of base/scripts (+ some space after script)");
+    }, "Width of scripted elements");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 5;
+      assert_greater_than_equal(getBox("msub").height, getBox("msubBase").height, e, "height is at least the one of the base");
+      assert_greater_than_equal(getBox("msup").height, getBox("msupBase").height, e, "height is at least the one of the base");
+      assert_greater_than_equal(getBox("msubsup").height, getBox("msubsupBase").height, e, "height is at least the one of the base");
+      assert_greater_than_equal(getBox("premsub").height, getBox("premsubBase").height, e, "height is at least the one of the base");
+      assert_greater_than_equal(getBox("premsup").height, getBox("premsupBase").height, e, "height is at least the one of the base");
+  assert_greater_than_equal(getBox("premsubsup").height, getBox("premsubsupBase").height, e, "height is at least the one of the base");
+
+      assert_approx_equals(getBox("msub").height, Math.max(getBox("msubSub").bottom, getBox("msubBase").bottom) - getBox("msubBase").top, e, "msub height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("msup").height, getBox("msupBase").bottom - Math.min(getBox("msupSup").top, getBox("msupBase").top), e, "msup height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("msubsup").height, Math.max(getBox("msubSub").bottom, getBox("msubBase").bottom) - Math.min(getBox("msupSup").top, getBox("msupBase").top), e, "msubsup height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("premsub").height, Math.max(getBox("premsubSub").bottom, getBox("premsubBase").bottom) - getBox("premsubBase").top, e, "msub height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("premsup").height, getBox("premsupBase").bottom - Math.min(getBox("premsupSup").top, getBox("premsupBase").top), e, "msup height is determined by the top/bottom sides of base/scripts");
+      assert_approx_equals(getBox("premsubsup").height, Math.max(getBox("premsubSub").bottom, getBox("premsubBase").bottom) - Math.min(getBox("premsupSup").top, getBox("premsupBase").top), e, "msubsup height is determined by the top/bottom sides of base/scripts");
+    }, "Height of scripted elements");
+
+    test(function() {
+      ["none", "mprescripts"].forEach(function(name) {
+        var elements = document.getElementsByTagName(name);
+        for (var i = 0; i < elements.length; i++) {
+          var box = elements[i].getBoundingClientRect();
+          assert_equals(box.height * box.width, 0, "<" + name + "> " + i + " has zero is empty");
+        }
+      });
+    }, "Size of empty elements");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <mmultiscripts id="msub" style="background: green">
+        <mspace id="msubBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubSub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <none/>
+      </mmultiscripts>
+      <mmultiscripts id="msup" style="background: green">
+        <mspace id="msupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <none/>
+        <mspace id="msupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="msubsup" style="background: green">
+        <mspace id="msubsupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubsupSub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="msubsupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="premsub" style="background: green">
+        <mspace id="premsubBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="premsubSub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <none/>
+      </mmultiscripts>
+      <mmultiscripts id="premsup" style="background: green">
+        <mspace id="premsupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <none/>
+        <mspace id="premsupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="premsubsup" style="background: green">
+        <mspace id="premsubsupBase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="premsubsupSub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="premsubsupSup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-3.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-3.html
new file mode 100644
index 0000000000..28db9b70cc
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-3.html
@@ -0,0 +1,192 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts metrics</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Basic metrics for the mmultiscript element with many scripts.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  math, mspace {
+    font: 25px/1 Ahem;
+  }
+</style>
+<script>
+  /* This test does not use a font with a MATH table and does not verify layout
+     rules in a very strict way. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      for (var i = 0; i < 5; i++)
+        assert_approx_equals(getBox("multi" + i + "base").middle, getBox("baseline").bottom, e, "base " + i + "is placed on the baseline");
+    }, "Alignment of the base on the baseline");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 5;
+      assert_approx_equals(getBox("multi0").width, 30, e, "width of multi0");
+      assert_approx_equals(getBox("multi0").height, 30, e, "height of multi0");
+      assert_approx_equals(getBox("multi1").width, 30, e, "width of multi1");
+      assert_approx_equals(getBox("multi1").height, 30, e, "height of multi1");
+      for (i = 2; i <= 4; i++) {
+        var scriptedBox = getBox("multi" + i);
+        var lastPostScript = getBox("multi" + i + "postsup" + (i - 1));
+        var firstPreScript = getBox("multi" + i + "presub1");
+        assert_approx_equals(scriptedBox.height, firstPreScript.bottom - lastPostScript.top, e, "height of multiscript" + i);
+        assert_approx_equals(scriptedBox.width, lastPostScript.right - firstPreScript.left, e, "width of multiscript" + i);
+      }
+    }, "Dimensions of the scripted elements");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 3;
+      for (var i = 2; i <= 4; i++) {
+        var base = getBox("multi" + i + "base");
+        for (var j = 1; j < i; j++) {
+          var presup = getBox("multi" + i + "presup" + j);
+          var postsup = getBox("multi" + i + "postsup" + j);
+          var presub = getBox("multi" + i + "presub" + j);
+          var postsub = getBox("multi" + i + "postsub" + j);
+          assert_approx_equals(base.top, presup.middle, e, "multi" + i + " " + j + " presup script");
+          assert_approx_equals(base.top, postsup.middle, e, "multi" + i + " " + j + " postsup script");
+          assert_approx_equals(base.bottom, presub.middle, e, "multi" + i + " " + j + " presub script");
+          assert_approx_equals(base.bottom, postsub.middle, e, "multi" + i + " " + j + " postsub script");
+        }
+      }
+    }, "Vertical positions of scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      for (var i = 2; i <= 4; i++) {
+        var base = getBox("multi" + i + "base");
+        for (var j = 1; j < i; j++) {
+          var presup = getBox("multi" + i + "presup" + j);
+          var postsup = getBox("multi" + i + "postsup" + j);
+          var presub = getBox("multi" + i + "presub" + j);
+          var postsub = getBox("multi" + i + "postsub" + j);
+          assert_approx_equals(presup.right, presub.right, e, "multi" + i + "pre");
+          assert_approx_equals(postsup.left, postsub.left, e, "multi" + i + "post");
+        }
+      }
+    }, "Horizontal alignment of scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 2; i <= 4; i++) {
+        var base = getBox("multi" + i + "base");
+        var firstPostScript = getBox("multi" + i + "postsub1");
+        var lastPreScript = getBox("multi" + i + "presup" + (i - 1));
+        assert_less_than_equal(base.right, firstPostScript.left, 1, "postcripts are after base");
+        assert_less_than_equal(lastPreScript.right, base.left, 1, "prescripts are before base");
+        assert_approx_equals(base.right, firstPostScript.left, 5, "spacing after base is not too large");
+        assert_approx_equals(lastPreScript.right, base.left, 5, "spacing before base is not too large");
+        for (var j = 1; j < i - 1; j++) {
+          var post = getBox("multi" + i + "postsub" + j);
+          var postNext = getBox("multi" + i + "postsub" + (j + 1));
+          var pre = getBox("multi" + i + "presup" + j);
+          var preNext = getBox("multi" + i + "presup" + (j + 1));
+          assert_less_than_equal(post.right, postNext.left, 1, "multi" + i + "order post" + j + " is before its successor");
+          assert_less_than_equal(pre.right, preNext.left, 1, "multi" + i + "order pre" + j + " is before its successor");
+          assert_approx_equals(post.right, postNext.left, 5, "multi" + i + "space after post" + j + " is not too large");
+          assert_approx_equals(pre.right, preNext.left, 5, "multi" + i + "space after pre" + j + " is not too large");
+        }
+      }
+    }, "Horizontal positions of scripts");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <mmultiscripts id="multi0" style="background: green">
+        <mspace id="multi0base" width="30px" height="15px" depth="15px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="multi1" style="background: green">
+        <mspace id="multi1base" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+      </mmultiscripts>
+      <mmultiscripts id="multi2" style="background: green">
+        <mspace id="multi2base" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="multi2postsub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi2postsup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi2presub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi2presup1" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="multi3" style="background: green">
+        <mspace id="multi3base" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="multi3postsub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3postsup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3postsub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3postsup2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi3presub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3presup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3presub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi3presup2" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="multi4" style="background: green">
+        <mspace id="multi4base" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="multi4postsub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4postsup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4postsub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4postsup2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4postsub3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4postsup3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi4presub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4presup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4presub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4presup2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4presub3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi4presup3" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <mmultiscripts id="multi5" style="background: green">
+        <mspace id="multi5base" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="multi5postsub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsup2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsub3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsup3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsub4" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5postsup4" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi5presub1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presup1" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presub2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presup2" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presub3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presup3" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presub4" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi5presup4" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-4.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-4.html
new file mode 100644
index 0000000000..cdf6cbe20e
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-4.html
@@ -0,0 +1,129 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts metrics</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Verify metrics of scripted elements for bases of different heights.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<style>
+  math, mspace {
+    font-size: 10px;
+  }
+</style>
+<script>
+  /* This test does not use any specific fonts and so the exact rules are not
+  specified precisely. We assume reasonable values for script shifts and
+  spacing. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", runTests);
+
+  var sizeArray = [50, 75, 100];
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      sizeArray.forEach(function(size) {
+         assert_approx_equals(getBox("msub" + size + "base").middle, getBox("baseline").bottom, e, "msub base " + size + "is placed on the baseline");
+         assert_approx_equals(getBox("msup" + size + "base").middle, getBox("baseline").bottom, e, "msup base " + size + "is placed on the baseline");
+         assert_approx_equals(getBox("msubsup" + size + "base").middle, getBox("baseline").bottom, e, "msubsup base " + size + "is placed on the baseline");
+         assert_approx_equals(getBox("multi" + size + "base").middle, getBox("baseline").bottom, e, "mmultiscripts base " + size + "is placed on the baseline");
+      });
+    }, "Alignment on the baseline for bases of different heights");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 5;
+      sizeArray.forEach(function(size) {
+         assert_approx_equals(getBox("msub" + size + "sub").middle, getBox("msub" + size + "base").bottom, e, "msub script " + size + "is placed at the top of of the base");
+      });
+    }, "Vertical position of the scripts for bases of different heights");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <msub id="msub50">
+        <mspace id="msub50base" width="30px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="msub50sub" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msub>
+      <msup id="msup50">
+        <mspace id="msup50base" width="30px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="msup50sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msup>
+      <msubsup id="msubsup50">
+        <mspace id="msubsup50base" width="30px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="msubsup50sub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="msubsup50sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msubsup>
+      <mmultiscripts id="multi50">
+        <mspace id="multi50base" width="30px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="multi50postsub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi50postsup" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi50presub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi50presup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <msub id="msub75">
+        <mspace id="msub75base" width="30px" height="75px" depth="75px" style="background: black"/>
+        <mspace id="msub75sub" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msub>
+      <msup id="msup75">
+        <mspace id="msup75base" width="30px" height="75px" depth="75px" style="background: black"/>
+        <mspace id="msup75sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msup>
+      <msubsup id="msubsup75">
+        <mspace id="msubsup75base" width="30px" height="75px" depth="75px" style="background: black"/>
+        <mspace id="msubsup75sub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="msubsup75sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msubsup>
+      <mmultiscripts id="multi75">
+        <mspace id="multi75base" width="30px" height="75px" depth="75px" style="background: black"/>
+        <mspace id="multi75postsub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi75postsup" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi75presub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi75presub" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+      <msub id="msub100">
+        <mspace id="msub100base" width="30px" height="100px" depth="100px" style="background: black"/>
+        <mspace id="msub100sub" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msub>
+      <msup id="msup100">
+        <mspace id="msup100base" width="30px" height="100px" depth="100px" style="background: black"/>
+        <mspace id="msup100sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msup>
+      <msubsup id="msubsup100">
+        <mspace id="msubsup100base" width="30px" height="100px" depth="100px" style="background: black"/>
+        <mspace id="msubsup100sub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="msubsup100sup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </msubsup>
+      <mmultiscripts id="multi100">
+        <mspace id="multi100base" width="30px" height="100px" depth="100px" style="background: black"/>
+        <mspace id="multi100postsub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi100postsup" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multi100presub" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="multi100presup" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-5.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-5.html
new file mode 100644
index 0000000000..1743c2e499
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-5.html
@@ -0,0 +1,97 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts metrics</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Verify metrics of scripted elements with tall scripts.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<style>
+  math, mspace {
+    font-size: 10px;
+  }
+</style>
+<script>
+  /* This test does not use any specific fonts and so the exact rules are not
+  specified precisely. We assume reasonable values for script shifts and
+  spacing. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", runTests);
+
+  var sizeArray = [50, 75, 100];
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+       assert_approx_equals(getBox("msubbase").middle, getBox("baseline").bottom, e, "msub base is placed on the baseline");
+       assert_approx_equals(getBox("msupbase").middle, getBox("baseline").bottom, e, "msup base is placed on the baseline");
+       assert_approx_equals(getBox("msubsupbase").middle, getBox("baseline").bottom, e, "msubsup base is placed on the baseline");
+       assert_approx_equals(getBox("multibase").middle, getBox("baseline").bottom, e, "mmultiscripts baseis placed on the baseline");
+    }, "Alignment on the baseline with different and large script heights");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      assert_greater_than(getBox("msubsub").top, getBox("msubbase").top, "msub: subscript is below the top of the base");
+      assert_less_than(getBox("msupsup").bottom, getBox("msupbase").bottom, "msup: supscript is above the bottom of the base");
+      assert_greater_than(getBox("msubsupsub").top, getBox("msubsupbase").top, "msubsup: subscript is below the top of the base");
+      assert_less_than(getBox("msubsupsup").bottom, getBox("msubsupbase").bottom, "msubsup: supscript is above the bottom of the base");
+      assert_greater_than(getBox("multipostsub").top, getBox("multibase").top, "mmultiscripts: postsubscript is below the top of the base");
+      assert_less_than(getBox("multipostsup").bottom, getBox("multibase").bottom, "mmultiscripts: postsupscript is above the bottom of the base");
+      assert_greater_than(getBox("multipresub").top, getBox("multibase").top, "mmultiscripts: presubscript is below the top of the base");
+      assert_less_than(getBox("multipresup").bottom, getBox("multibase").bottom, "mmultiscripts: presupscript is above the bottom of the base");
+    }, "Tall subscripts/superscripts are not placed too high/low");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      assert_greater_than(getBox("msubsupsub").top, getBox("msubsupsup").bottom, "msubsup: subscript is below the superscript");
+      assert_greater_than(getBox("multipresub").top, getBox("multipresup").bottom, "mmultiscripts: presubscript is below the presuperscript");
+      assert_greater_than(getBox("multipostsub").top, getBox("multipostsup").bottom, "mmultiscripts: postsubscript is below the postsuperscript");
+    }, "No collisions for tall subscripts and superscripts");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <msub id="msub">
+        <mspace id="msubbase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubsub" width="10px" height="50px" depth="50px" style="background: black"/>
+      </msub>
+      <msup id="msup">
+        <mspace id="msupbase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msupsup" width="10px" height="75px" depth="75px" style="background: black"/>
+      </msup>
+      <msubsup id="msubsup">
+        <mspace id="msubsupbase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="msubsupsub" width="10px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="msubsupsup" width="10px" height="75px" depth="75px" style="background: black"/>
+      </msubsup>
+      <mmultiscripts id="multi">
+        <mspace id="multibase" width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="multipostsub" width="10px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="multipostsup" width="10px" height="75px" depth="75px" style="background: black"/>
+        <mprescripts/>
+        <mspace id="multipresub" width="10px" height="50px" depth="50px" style="background: black"/>
+        <mspace id="multipresup" width="10px" height="75px" depth="75px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-6.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-6.html
new file mode 100644
index 0000000000..9666c80f9f
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-6.html
@@ -0,0 +1,120 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>mprescripts</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Position and size of mprescripts in mmultiscript element.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  math, mspace {
+    font: 25px/1 Ahem;
+  }
+</style>
+<script>
+  /* This test does not use a font with a MATH table and does not verify layout
+     rules in a very strict way. */
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+      Array.from(document.getElementsByTagName("mprescripts")).
+          forEach(prescript => {
+              let prescript_box = prescript.getBoundingClientRect();
+              let mmultiscripts = prescript.parentNode;
+              let name = mmultiscripts.getAttribute("data-name");
+              test(function() {
+                  assert_true(MathMLFeatureDetection.has_mspace());
+                  var e = 1;
+                  let base_box = mmultiscripts.firstElementChild.getBoundingClientRect();
+                  assert_approx_equals(prescript_box.left, base_box.left, e, `${name}, left`);
+                  assert_approx_equals((prescript_box.top + prescript_box.bottom) / 2, (base_box.top + base_box.bottom) / 2, e, `${name}, top`);
+
+                  if (name == "prescripts with padding/border/margin") {
+                      assert_approx_equals(prescript_box.width, 2*(15 + 25), e, `${name}, width`);
+                      assert_approx_equals(prescript_box.height, 2*(10 + 20), e, `${name}, height`);
+                  } else {
+                      assert_approx_equals(prescript_box.width, 0, e, `${name}, width`);
+                      assert_approx_equals(prescript_box.height, 0, e, `${name}, height`);
+                  }
+              }, `mprescripts coordinates and sizes (${name})`);
+          });
+
+      done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mmultiscripts data-name="2 postscripts">
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts data-name="2 prescripts">
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts data-name="2 prescripts, 4 postscripts">
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts data-name="4 prescripts, 2 postscripts">
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mmultiscripts data-name="prescripts with padding/border/margin">
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mprescripts style="background: blue;
+                            padding-top: 10px; border-top: 20px solid green;
+                            padding-bottom: 10px; border-bottom: 20px solid green;
+                            padding-left: 15px; border-left: 25px solid green;
+                            padding-right: 15px; border-right: 25px solid green;
+                            margin-top: 50px;"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+        <mspace width="30px" height="15px" depth="15px" style="background: black"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative-ref.html
new file mode 100644
index 0000000000..c1bf2e4695
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative-ref.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>msub/msup/msubsup/mmultiscripts subscriptshift and superscriptshift attributes (reference)</title>
+  </head>
+  <body>
+    <p>Test passes if the green squares are not about 300px away from the blue squares.</p>
+    <p>
+      <math>
+        <mmultiscripts>
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mprescripts/>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </mmultiscripts>
+        <msub>
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msub>
+        <msup>
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msup>
+        <msubsup>
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msubsup>
+      </math>
+    </p>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative.html
new file mode 100644
index 0000000000..2f29db401d
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-legacy-scriptshift-attributes-001.tentative.html
@@ -0,0 +1,48 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>msub/msup/msubsup/mmultiscripts subscriptshift and superscriptshift attributes</title>
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.msub">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.msup">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.msunsup">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.mmultiscripts">
+    <link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+    <link rel="help" href="https://w3c.github.io/mathml-core/#prescripts-and-tensor-indices-mmultiscripts">
+    <link rel="match" href="subsup-legacy-scriptshift-attributes-001.tentative-ref.html">
+  </head>
+  <body>
+    <p>Test passes if the green squares are not about 300px away from the blue squares.</p>
+    <p>
+      <math>
+        <mmultiscripts subscriptshift="300px" superscriptshift="300px">
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mprescripts/>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </mmultiscripts>
+        <msub subscriptshift="300px">
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msub>
+        <msup superscriptshift="300px">
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msup>
+        <msubsup subscriptshift="300px" superscriptshift="300px">
+          <mspace width="30px" height="30px" style="background: blue;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+          <mspace width="10px" height="10px" style="background: lightgreen;"></mspace>
+        </msubsup>
+      </math>
+    </p>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>
+      MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+      MathMLFeatureDetection.ensure_for_match_reftest("has_msubsup");
+      MathMLFeatureDetection.ensure_for_match_reftest("has_mmultiscripts");
+    </script>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-1.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-1.html
new file mode 100644
index 0000000000..3f49b1d53b
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-1.html
@@ -0,0 +1,354 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Elements msub, msup, subsup and msubsup correctly use the subscript and superscript parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: spaceafterscript3000;
+    src: url("/fonts/math/scripts-spaceafterscript3000.woff");
+  }
+  @font-face {
+    font-family: superscriptshiftup7000;
+    src: url("/fonts/math/scripts-superscriptshiftup7000.woff");
+  }
+  @font-face {
+    font-family: superscriptshiftupcramped5000;
+    src: url("/fonts/math/scripts-superscriptshiftupcramped5000.woff");
+  }
+  @font-face {
+    font-family: subscriptshiftdown6000;
+    src: url("/fonts/math/scripts-subscriptshiftdown6000.woff");
+  }
+  @font-face {
+    font-family: subsuperscriptgapmin11000;
+    src: url("/fonts/math/scripts-subsuperscriptgapmin11000.woff");
+  }
+  @font-face {
+    font-family: subsuperscriptgapmin11000superscriptbottommaxwithsubscript3000;
+    src: url("/fonts/math/scripts-subsuperscriptgapmin11000-superscriptbottommaxwithsubscript3000.woff");
+  }
+  @font-face {
+    font-family: subscripttopmax4000;
+    src: url("/fonts/math/scripts-subscripttopmax4000.woff");
+  }
+  @font-face {
+    font-family: superscriptbottommin8000;
+    src: url("/fonts/math/scripts-superscriptbottommin8000.woff");
+  }
+  @font-face {
+    font-family: subscriptbaselinedropmin9000;
+    src: url("/fonts/math/scripts-subscriptbaselinedropmin9000.woff");
+  }
+  @font-face {
+    font-family: superscriptbaselinedropmax10000;
+    src: url("/fonts/math/scripts-superscriptbaselinedropmax10000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("ref001").left - getBox("sub001").right, v, epsilon, "msub: Space after subscript");
+      assert_approx_equals(getBox("ref002").left - getBox("sup002").right, v, epsilon, "msup: Space after superscript");
+      assert_approx_equals(getBox("ref003").left - getBox("sup003").right, v, epsilon, "msubsup: Space after superscript");
+      assert_approx_equals(getBox("sup0042").left - getBox("sup0041").right, v, epsilon, "mmultiscripts: Space after first superscript");
+      assert_approx_equals(getBox("sup0043").left - getBox("sup0042").right, v, epsilon, "mmultiscripts: Space after second superscript");
+      assert_approx_equals(getBox("ref004").left - getBox("sup0043").right, v, epsilon, "mmultiscripts: Space after last superscript");
+    }, "SpaceAfterScript");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref101").bottom - getBox("sup102").bottom, v, epsilon, "msup: Superscript shift");
+      assert_approx_equals(getBox("ref101").bottom - getBox("sup103").bottom, v, epsilon, "msubsup: Superscript shift");
+      assert_approx_equals(getBox("ref101").bottom - getBox("sup1041").bottom, v, epsilon, "mmultiscripts: First superscript shift");
+      assert_approx_equals(getBox("ref101").bottom - getBox("sup1042").bottom, v, epsilon, "mmultiscripts: Second superscript shift");
+      assert_approx_equals(getBox("ref101").bottom - getBox("sup1043").bottom, v, epsilon, "mmultiscripts: Last superscript shift");
+    }, "SuperscriptShiftUp");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref201").bottom - getBox("sup202").bottom, v, epsilon, "msup: Superscript shift");
+      assert_approx_equals(getBox("ref201").bottom - getBox("sup203").bottom, v, epsilon, "msubsup: Superscript shift");
+      assert_approx_equals(getBox("ref201").bottom - getBox("sup2041").bottom, v, epsilon, "mmultiscripts: First superscript shift");
+      assert_approx_equals(getBox("ref201").bottom - getBox("sup2042").bottom, v, epsilon, "mmultiscripts: Second superscript shift");
+      assert_approx_equals(getBox("ref201").bottom - getBox("sup2043").bottom, v, epsilon, "mmultiscripts: Last superscript shift");
+    }, "SuperscriptShiftUpCramped");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 6000 * emToPx;
+      assert_approx_equals(getBox("sub301").bottom - getBox("ref300").bottom, v, epsilon, "msup: Subscript shift");
+      assert_approx_equals(getBox("sub302").bottom - getBox("ref300").bottom, v, epsilon, "msubsup: Subscript shift");
+      assert_approx_equals(getBox("sub303").bottom - getBox("ref300").bottom, v, epsilon, "mmultiscripts: First subscript shift");
+      assert_approx_equals(getBox("sub304").bottom - getBox("ref300").bottom, v, epsilon, "mmultiscripts: Second subscript shift");
+    }, "SubscriptShiftDown");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 11000 * emToPx;
+      assert_approx_equals(getBox("sub4011").top - getBox("sup4012").bottom, v, epsilon, "msubsup: SubSuperscript gap");
+      assert_approx_equals(getBox("sub4021").top - getBox("sup4022").bottom, v, epsilon, "mmultiscripts: SubSuperscript gap");
+    }, "SubSuperscriptGapMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v1 = 11000 * emToPx;
+      var v2 = 3000 * emToPx;
+      assert_approx_equals(getBox("sub501").top - getBox("sup501").bottom, v1, epsilon, "msubsup: SubSuperscript gap");
+      assert_approx_equals(getBox("ref500").bottom - getBox("sup501").bottom, v2, epsilon, "msubsup: Superscript bottom");
+      assert_approx_equals(getBox("sub502").top - getBox("sup502").bottom, v1, epsilon, "mmultiscripts: SubSuperscript gap");
+      assert_approx_equals(getBox("ref500").bottom - getBox("sup502").bottom, v2, epsilon, "mmultiscripts: Superscript bottom");
+    }, "SuperscriptBottomMaxWithSubscript");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 4000 * emToPx;
+      assert_approx_equals(getBox("ref600").bottom - getBox("sub601").top, v, epsilon, "msub: Subscript top");
+    }, "SubscriptTopMax");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 8000 * emToPx;
+      assert_approx_equals(getBox("ref700").bottom - getBox("sub701").bottom, v, epsilon, "msub: Superscript bottom");
+    }, "SuperscriptBottomMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 9000 * emToPx;
+      assert_approx_equals(getBox("sub801").bottom - getBox("base801").bottom, v, epsilon, "msub: Superscript drop");
+    }, "SubscriptBaselineDrop");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 10000 * emToPx;
+      assert_approx_equals(getBox("sup901").bottom - getBox("base901").top, v, epsilon, "msup: Superscript drop");
+    }, "SuperscriptBaselineDrop");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: spaceafterscript3000;">
+        <msub>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub001" height="1em" width="1em" style="background: red"/>
+        </msub>
+        <mspace id="ref001" height="1em" width="1em" style="background: green"/>
+      </math>
+      <math style="font-family: spaceafterscript3000;">
+        <msup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sup002" height="1em" width="1em" style="background: red"/>
+        </msup>
+        <mspace id="ref002" height="1em" width="1em" style="background: green"/>
+      </math>
+      <math style="font-family: spaceafterscript3000;">
+        <msubsup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace/>
+          <mspace id="sup003" height="1em" width="1em" style="background: red"/>
+        </msubsup>
+        <mspace id="ref003" height="1em" width="1em" style="background: green"/>
+      </math>
+      <math style="font-family: spaceafterscript3000;">
+        <mmultiscripts>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <none/>
+          <mspace id="sup0041" height="1em" width="1em" style="background: red"/>
+          <none/>
+          <mspace id="sup0042" height="1em" width="1em" style="background: red"/>
+          <none/>
+          <mspace id="sup0043" height="1em" width="1em" style="background: red"/>
+        </mmultiscripts>
+        <mspace id="ref004" height="1em" width="1em" style="background: green"/>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: superscriptshiftup7000;">
+        <mspace id="ref101" height="1em" width="1em" style="background: green"/>
+        <msup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sup102" height="1em" width="1em" style="background: red"/>
+        </msup>
+        <msubsup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace height="1em" width="1em" style="background: red"/>
+          <mspace id="sup103" height="1em" width="1em" style="background: red"/>
+        </msubsup>
+        <mmultiscripts>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <none/>
+          <mspace id="sup1041" height="1em" width="1em" style="background: red"/>
+          <none/>
+          <mspace id="sup1042" height="1em" width="1em" style="background: red"/>
+          <none/>
+          <mspace id="sup1043" height="1em" width="1em" style="background: red"/>
+        </mmultiscripts>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: superscriptshiftupcramped5000;">
+        <msqrt>
+          <mspace id="ref201" height="1em" width="1em" style="background: green"/>
+          <msup>
+            <mspace height="2em" width="2em" style="background: blue"/>
+            <mspace id="sup202" height="1em" width="1em" style="background: red"/>
+          </msup>
+          <msubsup>
+            <mspace height="2em" width="2em" style="background: blue"/>
+            <mspace height="1em" width="1em" style="background: blue"/>
+            <mspace id="sup203" height="1em" width="1em" style="background: red"/>
+          </msubsup>
+          <mmultiscripts>
+            <mspace height="2em" width="2em" style="background: blue"/>
+            <none/>
+            <mspace id="sup2041" height="1em" width="1em" style="background: red"/>
+            <none/>
+            <mspace id="sup2042" height="1em" width="1em" style="background: red"/>
+            <none/>
+            <mspace id="sup2043" height="1em" width="1em" style="background: red"/>
+          </mmultiscripts>
+        </msqrt>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: subscriptshiftdown6000;">
+        <mspace id="ref300" height="1em" width="1em" style="background: green"/>
+        <msub>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub301" height="1em" width="1em" style="background: red"/>
+        </msub>
+        <msubsup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub302" height="1em" width="1em" style="background: red"/>
+          <mspace height="1em" width="1em" style="background: blue"/>
+        </msubsup>
+        <mmultiscripts>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub303" height="1em" width="1em" style="background: red"/>
+          <none/>
+          <mspace id="sub304" height="1em" width="1em" style="background: red"/>
+          <none/>
+        </mmultiscripts>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: subsuperscriptgapmin11000;">
+        <msubsup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub4011" height="1em" width="1em" style="background: red"/>
+          <mspace id="sup4012" height="1em" width="1em" style="background: red"/>
+        </msubsup>
+        <mmultiscripts>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <none/>
+          <none/>
+          <mspace id="sub4021" height="1em" width="1em" style="background: red"/>
+          <mspace id="sup4022" height="1em" width="1em" style="background: red"/>
+        </mmultiscripts>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: subsuperscriptgapmin11000superscriptbottommaxwithsubscript3000;">
+        <mspace id="ref500" height="1em" width="1em" style="background: green"/>
+        <msubsup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub501" height="1em" width="1em" style="background: red"/>
+          <mspace id="sup501" height="1em" width="1em" style="background: red"/>
+        </msubsup>
+        <mmultiscripts>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <none/>
+          <none/>
+          <mspace id="sub502" height="1em" width="1em" style="background: red"/>
+          <mspace id="sup502" height="1em" width="1em" style="background: red"/>
+        </mmultiscripts>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: subscripttopmax4000;">
+        <mspace id="ref600" height="1em"
+                width="1em" style="background: green"/>
+        <msub>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub601" height="10em"
+                  width="1em" style="background: red"/>
+        </msub>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: superscriptbottommin8000;">
+        <mspace id="ref700" height="1em"
+                width="1em" style="background: green"/>
+        <msup>
+          <mspace height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub701" depth="1em"
+                  width="1em" style="background: red"/>
+        </msup>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: subscriptbaselinedropmin9000;">
+        <msub>
+          <mspace id="base801" height="2em" width="2em" style="background: blue"/>
+          <mspace id="sub801" height="1em"
+                  width="1em" style="background: red"/>
+        </msub>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: superscriptbaselinedropmax10000;">
+        <msup>
+          <mspace id="base901" height="15em" width="2em" style="background: blue"/>
+          <mspace id="sup901" height="1em"
+                  width="1em" style="background: red"/>
+        </msup>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-2.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-2.html
new file mode 100644
index 0000000000..205697f4e4
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/subsup-parameters-2.html
@@ -0,0 +1,181 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Subscripts and Superscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#subscripts-and-superscripts-msub-msup-msubsup">
+<meta name="assert" content="Elements msub, msup, subsup and msubsup correctly use the italic correction from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: largeop-displayoperatorminheight5000;
+    src: url("/fonts/math/largeop-displayoperatorminheight5000.woff");
+  }
+  @font-face {
+    font-family: largeop-displayoperatorminheight2000-2AFF-italiccorrection3000;
+    src: url("/fonts/math/largeop-displayoperatorminheight2000-2AFF-italiccorrection3000.woff");
+  }
+  @font-face {
+    font-family: largeop-displayoperatorminheight7000-2AFF-italiccorrection5000;
+    src: url("/fonts/math/largeop-displayoperatorminheight7000-2AFF-italiccorrection5000.woff");
+  }
+</style>
+<script>
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  /*
+    These two tests verify that:
+    - In msub, the script is at the right of the base minus the italic correction.
+    - In msup, the script is just at the right of the base.
+    - In msubsup, the scripts are shifted by the italic correction.
+    - In mmultiscripts, postscript pairs are shifted by the italic correction.
+    - In mmultiscripts, prescript pairs are vertically aligned.
+  */
+  var epsilon = 1;
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 0;
+      assert_approx_equals(getBox("base001").right - getBox("sub001").left, v, epsilon, "msub");
+      assert_approx_equals(getBox("sup002").left, getBox("base002").right, epsilon, "msup");
+      assert_approx_equals(getBox("sup003").left - getBox("sub003").left, v, epsilon, "msubsup");
+      assert_approx_equals(getBox("sup004").left - getBox("sub004").left, v, epsilon, "mmultiscripts postscripts");
+      assert_approx_equals(getBox("sup005").left - getBox("sub005").left, 0, epsilon, "mmultiscripts prescripts");
+    }, "Null Italic Correction");
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("base011").right - getBox("sub011").left, v, epsilon, "msub");
+      assert_approx_equals(getBox("sup012").left, getBox("base012").right, epsilon, "msup");
+      assert_approx_equals(getBox("sup013").left - getBox("sub013").left, v, epsilon, "msubsup");
+      assert_approx_equals(getBox("sup014").left - getBox("sub014").left, v, epsilon, "mmultiscripts postscripts");
+      assert_approx_equals(getBox("sup015").left - getBox("sub015").left, 0, epsilon, "mmultiscripts prescripts");
+    }, "NonNull Italic Correction (MathGlyphVariantRecord)");
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("base021").right - getBox("sub021").left, v, epsilon, "msub");
+      assert_approx_equals(getBox("sup022").left, getBox("base022").right, epsilon, "msup");
+      assert_approx_equals(getBox("sup023").left - getBox("sub023").left, v, epsilon, "msubsup");
+      assert_approx_equals(getBox("sup024").left - getBox("sub024").left, v, epsilon, "mmultiscripts postscripts");
+      assert_approx_equals(getBox("sup025").left - getBox("sub025").left, 0, epsilon, "mmultiscripts prescripts");
+    }, "NonNull Italic Correction (GlyphAssembly)");
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <h2>Null Italic Correction</h2>
+  <p>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight5000;">
+      <msub>
+        <mo id="base001" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub001" height="1em" width="1em" style="background: blue"/>
+      </msub>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight5000;">
+      <msup>
+        <mo id="base002" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sup002" height="1em" width="1em" style="background: blue"/>
+      </msup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight5000;">
+      <msubsup>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub003" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup003" height="1em" width="1em" style="background: green"/>
+      </msubsup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight5000;">
+      <mmultiscripts>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub004" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup004" height="1em" width="1em" style="background: green"/>
+        <mprescripts/>
+        <mspace id="sub005" height="1em" width="1em" style="background: magenta"/>
+        <mspace id="sup005" height="1em" width="1em" style="background: cyan"/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <h2>NonNull Italic Correction (MathGlyphVariantRecord)</h2>
+  <p>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight2000-2AFF-italiccorrection3000;">
+      <msub>
+        <mo id="base011" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub011" height="1em" width="1em" style="background: blue"/>
+      </msub>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight2000-2AFF-italiccorrection3000;">
+      <msup>
+        <mo id="base012" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sup012" height="1em" width="1em" style="background: blue"/>
+      </msup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight2000-2AFF-italiccorrection3000;">
+      <msubsup>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub013" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup013" height="1em" width="1em" style="background: green"/>
+      </msubsup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight2000-2AFF-italiccorrection3000;">
+      <mmultiscripts>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub014" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup014" height="1em" width="1em" style="background: green"/>
+        <mprescripts/>
+        <mspace id="sub015" height="1em" width="1em" style="background: magenta"/>
+        <mspace id="sup015" height="1em" width="1em" style="background: cyan"/>
+      </mmultiscripts>
+    </math>
+  </p>
+  <h2>NonNull Italic Correction (GlyphAssembly)</h2>
+  <p>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight7000-2AFF-italiccorrection5000;">
+      <msub>
+        <mo id="base021" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub021" height="1em" width="1em" style="background: blue"/>
+      </msub>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight7000-2AFF-italiccorrection5000;">
+      <msup>
+        <mo id="base022" lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sup022" height="1em" width="1em" style="background: blue"/>
+      </msup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight7000-2AFF-italiccorrection5000;">
+      <msubsup>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub023" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup023" height="1em" width="1em" style="background: green"/>
+      </msubsup>
+    </math>
+    <math displaystyle="true" style="font-family: largeop-displayoperatorminheight7000-2AFF-italiccorrection5000;">
+      <mmultiscripts>
+        <mo lspace="0px" rspace="0px">&#x2AFF;</mo>
+        <mspace id="sub024" height="1em" width="1em" style="background: blue"/>
+        <mspace id="sup024" height="1em" width="1em" style="background: green"/>
+        <mprescripts/>
+        <mspace id="sub025" height="1em" width="1em" style="background: magenta"/>
+        <mspace id="sup025" height="1em" width="1em" style="background: cyan"/>
+      </mmultiscripts>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-1.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-1.html
new file mode 100644
index 0000000000..ae4a945404
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-1.html
@@ -0,0 +1,175 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover correctly .">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<link rel="stylesheet" type="text/css" href="/fonts/ahem.css" />
+<style>
+  math, mspace, mo {
+    font-family: Ahem;
+    font-size: 10px;
+  }
+</style>
+<script>
+  /* This test does not use any specific fonts and so the exact rules are not
+  specified precisely. We assume reasonable values for script shifts and
+  spacing. */
+
+  function getBox(aId) {
+    var box = document.getElementById(aId).getBoundingClientRect();
+    box.middle = (box.bottom + box.top) / 2;
+    box.center = (box.left + box.right) / 2;
+    return box;
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      for (var i = 0; i <= 3; i++) {
+        assert_approx_equals(getBox("under" + i + "base").middle, getBox("baseline").bottom, e, "munder " + i + ": base is placed on the baseline");
+        assert_approx_equals(getBox("over" + i + "base").middle, getBox("baseline").bottom, e, "mover " + i + ": base is placed on the baseline");
+      }
+      for (var i = 0; i <= 5; i++) {
+        assert_approx_equals(getBox("underover" + i + "base").middle, getBox("baseline").bottom, e, "munderover " + i + ": base is placed on the baseline");
+      }
+    }, "Alignment of the base on the baseline");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      for (var i = 0; i <= 3; i++) {
+        assert_approx_equals(getBox("under" + i + "under").center, getBox("under" + i + "base").center, e, "munder " + i + ": base and script are horizontally centered");
+        assert_approx_equals(getBox("over" + i + "over").center, getBox("over" + i + "base").center, e, "mover " + i + ": base and script are horizontally centered");
+      }
+      for (var i = 0; i <= 5; i++) {
+        assert_approx_equals(getBox("underover" + i + "under").center, getBox("underover" + i + "base").center, e, "munderover " + i + ": base and underscript are horizontally centered");
+        assert_approx_equals(getBox("underover" + i + "over").center, getBox("underover" + i + "base").center, e, "munderover " + i + ": base and overscript are horizontally centered");
+      }
+    }, "Horizontal alignments of base and scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 0; i <= 3; i++) {
+        assert_greater_than_equal(getBox("under" + i + "under").top, getBox("under" + i + "base").bottom, "munder " + i + ": script is under base");
+        assert_less_than_equal(getBox("over" + i + "over").bottom, getBox("over" + i + "base").top, "mover " + i + ": script is over base");
+      }
+      for (var i = 0; i <= 5; i++) {
+        assert_greater_than_equal(getBox("underover" + i + "under").top, getBox("underover" + i + "base").bottom, "munderover " + i + ": underscript is under base");
+        assert_less_than_equal(getBox("underover" + i + "over").bottom, getBox("underover" + i + "base").top, "munderover " + i + ": overscript is over base");
+      }
+    }, "Relative vertical positions of base and scripts");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 1;
+      for (var i = 0; i <= 3; i++) {
+        assert_approx_equals(getBox("under" + i).width, Math.max(getBox("under" + i + "base").width, getBox("under" + i + "under").width), e, "munder " + i + ": width is determined by the maximum of width of base and script");
+        assert_approx_equals(getBox("over" + i).width, Math.max(getBox("over" + i + "base").width, getBox("over" + i + "over").width), e, "mover " + i + ": width is determined by the maximum of width of base and script");
+      }
+      for (var i = 0; i <= 5; i++) {
+        assert_approx_equals(getBox("underover" + i).width, Math.max(getBox("underover" + i + "base").width, getBox("underover" + i + "under").width, getBox("underover" + i + "over").width), e, "munderover " + i + ": width is determined by the maximum of width of base and scripts");
+      }
+    }, "Width of scripted elements");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var e = 4;
+      for (var i = 0; i <= 3; i++) {
+        assert_approx_equals(getBox("under" + i).height, getBox("under" + i + "base").height + getBox("under" + i + "under").height, e, "munder " + i + ": height is determined by the sum of heights of base and script plus some spacing.");
+        assert_approx_equals(getBox("over" + i).height, getBox("over" + i + "base").height + getBox("over" + i + "over").height, e, "mover " + i + ": height is determined by the sum of heights of base and script plus some spacing.");
+      }
+      for (var i = 0; i <= 5; i++) {
+        assert_approx_equals(getBox("underover" + i).height, getBox("underover" + i + "base").height + getBox("underover" + i + "under").height + getBox("underover" + i + "over").height, e, "munderover " + i + ": height is determined by the sum heights of base and scripts");
+      }
+    }, "Height of scripted elements");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+  <p>
+    <math>
+      <mspace id="baseline" width="30px" height="2px" depth="0px" style="background: blue"/>
+      <munder id="under0">
+        <mspace id="under0base" width="30px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="under0under" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munder>
+      <munder id="under1">
+        <mspace id="under1base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="under1under" width="30px" height="5px" depth="5px" style="background: black"/>
+      </munder>
+      <munder id="under2">
+        <mspace id="under2base" width="10px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="under2under" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munder>
+      <munder id="under3">
+        <mspace id="under3base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="under3under" width="10px" height="15px" depth="15px" style="background: black"/>
+      </munder>
+      <mover id="over0">
+        <mspace id="over0base" width="30px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="over0over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mover>
+      <mover id="over1">
+        <mspace id="over1base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="over1over" width="30px" height="5px" depth="5px" style="background: black"/>
+      </mover>
+      <mover id="over2">
+        <mspace id="over2base" width="10px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="over2over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </mover>
+      <mover id="over3">
+        <mspace id="over3base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="over3over" width="10px" height="15px" depth="15px" style="background: black"/>
+      </mover>
+      <munderover id="underover0">
+        <mspace id="underover0base" width="30px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover0under" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover0over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munderover>
+      <munderover id="underover1">
+        <mspace id="underover1base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover1under" width="30px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover1over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munderover>
+      <munderover id="underover2">
+        <mspace id="underover2base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover2under" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover2over" width="30px" height="5px" depth="5px" style="background: black"/>
+      </munderover>
+      <munderover id="underover3">
+        <mspace id="underover3base" width="10px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="underover3under" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover3over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munderover>
+      <munderover id="underover4">
+        <mspace id="underover4base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover4under" width="10px" height="15px" depth="15px" style="background: black"/>
+        <mspace id="underover4over" width="10px" height="5px" depth="5px" style="background: black"/>
+      </munderover>
+      <munderover id="underover5">
+        <mspace id="underover5base" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover5under" width="10px" height="5px" depth="5px" style="background: black"/>
+        <mspace id="underover5over" width="10px" height="15px" depth="15px" style="background: black"/>
+      </munderover>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001-ref.html
new file mode 100644
index 0000000000..a9545c60f4
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001-ref.html
@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>munder/mover/munderover align (reference)</title>
+  </head>
+  <body>
+    <p>Test passes if the center of the following rectangles is aligned
+      on the same vertical axis.</p>
+    <p>
+      <math>
+        <munder>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munder>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munder>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munder>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mover>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </mover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mover>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </mover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munderover>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munderover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munderover>
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munderover>
+      </math>
+    </p>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001.html
new file mode 100644
index 0000000000..aa2460e062
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-legacy-align-attribute-001.html
@@ -0,0 +1,72 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <title>munder/mover/munderover align</title>
+    <link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.munder">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.mover">
+    <link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.munderover">
+    <meta name="assert" content="Check that the legacy align attribute is ignored.">
+    <link rel="match" href="underover-legacy-align-attribute-001-ref.html">
+  </head>
+  <body>
+    <p>Test passes if the center of the following rectangles is aligned
+      on the same vertical axis.</p>
+    <p>
+      <math>
+        <munder align="left">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munder>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munder align="right">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munder>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mover align="left">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </mover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <mover align="right">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </mover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munderover align="left">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munderover>
+      </math>
+    </p>
+    <p>
+      <math>
+        <munderover align="right">
+          <mspace width="30px" height="20px" style="background: cyan;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+          <mspace width="10px" height="20px" style="background: blue;"></mspace>
+        </munderover>
+      </math>
+    </p>
+    <script src="/mathml/support/feature-detection.js"></script>
+    <script>
+      MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+      MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+    </script>
+  </body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-1.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-1.html
new file mode 100644
index 0000000000..eb2e0512e0
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-1.html
@@ -0,0 +1,151 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover correctly use the limit parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: lowerlimitbaselinedropmin3000;
+    src: url("/fonts/math/limits-lowerlimitbaselinedropmin3000.woff");
+  }
+  @font-face {
+    font-family: lowerlimitgapmin11000;
+    src: url("/fonts/math/limits-lowerlimitgapmin11000.woff");
+  }
+  @font-face {
+    font-family: upperlimitbaselinerisemin5000;
+    src: url("/fonts/math/limits-upperlimitbaselinerisemin5000.woff");
+  }
+  @font-face {
+    font-family: upperlimitgapmin7000;
+    src: url("/fonts/math/limits-upperlimitgapmin7000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("under00011").top - getBox("ref0001").bottom,
+                           v, epsilon, "munder: under shift");
+      assert_approx_equals(getBox("under00012").top - getBox("ref0001").bottom,
+                           v, epsilon, "munderover: under shift");
+    }, "LowerLimitBaselineDropMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 11000 * emToPx;
+      assert_approx_equals(getBox("under00021").top - getBox("ref0002").bottom,
+                           v, epsilon, "munder: under gap");
+      assert_approx_equals(getBox("under00022").top - getBox("ref0002").bottom,
+                           v, epsilon, "munderover: under gap");
+    }, "LowerLimitGapMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref0003").top - getBox("over00031").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0003").top - getBox("over00032").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "UpperLimitBaselineRiseMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref0004").top - getBox("over00041").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0004").top - getBox("over00042").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "UpperLimitGapMin");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: lowerlimitbaselinedropmin3000;">
+        <mspace id="ref0001" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="under00011" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="under00012" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: lowerlimitgapmin11000;">
+        <mspace id="ref0002" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="under00021" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="under00022" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: upperlimitbaselinerisemin5000;">
+        <mspace id="ref0003" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="over00031" height="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00032" height="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: upperlimitgapmin7000;">
+        <mspace id="ref0004" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace id="over00041" depth="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mo movablelimits="false">&#x2211;</mo>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00042" depth="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-2.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-2.html
new file mode 100644
index 0000000000..aad03a3863
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-2.html
@@ -0,0 +1,151 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover correctly use the stretch stack parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: bottomshiftdown3000;
+    src: url("/fonts/math/stretchstack-bottomshiftdown3000.woff");
+  }
+  @font-face {
+    font-family: gapbelowmin11000;
+    src: url("/fonts/math/stretchstack-gapbelowmin11000.woff");
+  }
+  @font-face {
+    font-family: topshiftup5000;
+    src: url("/fonts/math/stretchstack-topshiftup5000.woff");
+  }
+  @font-face {
+    font-family: gapabovemin7000;
+    src: url("/fonts/math/stretchstack-gapabovemin7000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("under00011").top - getBox("ref0001").bottom,
+                           v, epsilon, "munder: under shift");
+      assert_approx_equals(getBox("under00012").top - getBox("ref0001").bottom,
+                           v, epsilon, "munderover: under shift");
+    }, "StretchStackBottomShiftDown");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 11000 * emToPx;
+      assert_approx_equals(getBox("under00021").top - getBox("ref0002").bottom,
+                           v, epsilon, "munder: under gap");
+      assert_approx_equals(getBox("under00022").top - getBox("ref0002").bottom,
+                           v, epsilon, "munderover: under gap");
+    }, "StretchStackGapBelowMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref0003").top - getBox("over00031").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0003").top - getBox("over00032").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "StretchStackTopShiftUp");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref0004").top - getBox("over00041").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0004").top - getBox("over00042").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "StretchStackGapAboveMin");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: bottomshiftdown3000;">
+        <mspace id="ref0001" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mo>&#x2192;</mo>
+          <mspace id="under00011" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mo>&#x2192;</mo>
+          <mspace id="under00012" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: gapbelowmin11000;">
+        <mspace id="ref0002" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mo>&#x2192;</mo>
+          <mspace id="under00021" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mo>&#x2192;</mo>
+          <mspace id="under00022" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: topshiftup5000;">
+        <mspace id="ref0003" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mo>&#x2192;</mo>
+          <mspace id="over00031" height="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mo>&#x2192;</mo>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00032" height="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: gapabovemin7000;">
+        <mspace id="ref0004" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mo>&#x2192;</mo>
+          <mspace id="over00041" depth="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mo>&#x2192;</mo>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00042" depth="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-3.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-3.html
new file mode 100644
index 0000000000..9ec9dbf47e
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-3.html
@@ -0,0 +1,452 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover correctly use underbar/overbar and AccentBaseHeight parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: accentbaseheight4000underbarextradescender5000;
+    src: url("/fonts/math/underover-accentbaseheight4000-underbarextradescender5000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000underbarverticalgap7000;
+    src: url("/fonts/math/underover-accentbaseheight4000-underbarverticalgap7000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000overbarextraascender3000;
+    src: url("/fonts/math/underover-accentbaseheight4000-overbarextraascender3000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000overbarverticalgap11000;
+    src: url("/fonts/math/underover-accentbaseheight4000-overbarverticalgap11000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 2;
+  var axisBaseHeight = 4000 *  emToPx;
+  var shortBaseHeight = 3000 * emToPx; // shortBaseHeight < axisBaseHeight
+  var tallBaseHeight = 5000 * emToPx; // tallBaseHeight > axisBaseHeight
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function getBooleanValue(element, name) {
+      return (element.getAttribute(name) || "").toLowerCase() === "true";
+  }
+  let dynamicBooleanAttributeChanges = {
+      "Invert boolean value using absent attribute": function(element, name) {
+          if (getBooleanValue(element, name)) {
+              element.removeAttribute(name);
+          } else {
+              element.setAttribute(name, "true");
+          }
+      },
+
+      "Invert boolean value using invalid attribute": function(element, name) {
+          if (getBooleanValue(element, name)) {
+              element.setAttribute(name, "invalid");
+          } else {
+              element.setAttribute(name, "true");
+          }
+      },
+
+      "Change case of boolean attribute": function(element, name) {
+          if (getBooleanValue(element, name)) {
+              element.setAttribute(name, "TrUe");
+          } else {
+              element.setAttribute(name, "FaLsE");
+          }
+      }
+  };
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 1; i <= 4; i++) {
+        for (var j = 1; j <= 6; j++) {
+           var baseId = ("base00" + i) + j;
+           assert_approx_equals(getBox("ref00" + i).bottom,
+                                getBox(baseId).bottom,
+                                epsilon,
+                                "alignment of " + baseId);
+        }
+      }
+    }, "Baseline alignment");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 1; i <= 4; i++) {
+        for (var j = 1; j <= 6; j++) {
+           var baseId = ("base00" + i) + j;
+           assert_approx_equals(getBox(baseId).height,
+                                j == 2 || j == 5 ?
+                                tallBaseHeight :shortBaseHeight,
+                                epsilon,
+                                "height of " + baseId);
+        }
+      }
+    }, "Heights of bases");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0014").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0015").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0016").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el001" + j;
+        var baseId = "base001" + j;
+        var underId = "under001" + j;
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             0, epsilon,
+                             "gap between " + baseId + " and " + underId);
+        assert_approx_equals(getBox(elId).bottom - getBox(underId).bottom,
+                             v, epsilon,
+                             "extra descender below " + underId);
+      }
+    }, "AccentBaseHeight, UnderbarExtraDescender");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0024").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0025").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0026").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el002" + j;
+        var baseId = "base002" + j;
+        var underId = "under002" + j;
+        var gap = (j == 2 || j == 3 ? 0 : v);
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             gap, epsilon,
+                             "gap between " + baseId + " and " + underId);
+      }
+    }, "AccentBaseHeight, UnderbarVerticalGap");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0031").bottom,
+                           shortBaseHeight, epsilon,
+                           "mover: nonaccent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0032").bottom,
+                           tallBaseHeight, epsilon,
+                           "mover: accent over tall base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0033").bottom,
+                           axisBaseHeight, epsilon,
+                           "mover: accent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0034").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0035").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0036").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el003" + j;
+        var baseId = "base003" + j;
+        if (j >= 4) {
+          var underId = "under003" + j;
+          assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                               0, epsilon,
+                               "gap between " + baseId + " and " + underId);
+        }
+        var overId = "over003" + j;
+        assert_approx_equals(getBox(overId).top - getBox(elId).top,
+                             v, epsilon,
+                             "extra ascender below " + overId);
+      }
+    }, "AccentBaseHeight, OverbarExtraAscender");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      v = 11000 * emToPx;
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0041").bottom,
+                           shortBaseHeight + v, epsilon,
+                           "mover: nonaccent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0042").bottom,
+                           tallBaseHeight, epsilon,
+                           "mover: accent over tall base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0043").bottom,
+                           axisBaseHeight, epsilon,
+                           "mover: accent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0044").bottom,
+                           shortBaseHeight + v, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0045").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0046").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 4; j <= 6; j++) {
+        var baseId = "base004" + j;
+        var underId = "under004" + j;
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             0, epsilon,
+                             "gap between " + baseId + " and " + underId);
+      }
+    }, "AccentBaseHeight, OverbarVerticalGap");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+      var v = 7000 * emToPx;
+
+      for (var j = 1; j <= 4; j++) {
+        var elId = `el005${j}`;
+        var baseId = `base005${j}`;
+        var underId = `under005${j}`;
+
+        for (name in dynamicBooleanAttributeChanges) {
+            let element = document.getElementById(elId);
+            dynamicBooleanAttributeChanges[name](element, "accentunder");
+            var value =  getBooleanValue(element, "accentunder");
+            var gap = value ? 0 : v;
+            assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                                 gap, epsilon,
+                                 `${elId}: gap between base and underscript ; ${name}`);
+        };
+      }
+    }, "Dynamic change of accentunder attribute");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+      v = 11000 * emToPx;
+      for (var j = 1; j <= 4; j++) {
+        var elId = `el006${j}`;
+        var refId = `base006${j}`;
+        var overId = `over006${j}`;
+        for (name in dynamicBooleanAttributeChanges) {
+            let element = document.getElementById(elId);
+            dynamicBooleanAttributeChanges[name](element, "accent");
+            var value =  getBooleanValue(element, "accent");
+            assert_approx_equals(getBox(refId).bottom - getBox(overId).bottom,
+                                 value ? axisBaseHeight : shortBaseHeight + v,
+                                 epsilon,
+                                 `${elId}: accent=${value} ; short base ; ${name}`);
+        }
+      }
+    }, "Dynamic change of accent attribute");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: accentbaseheight4000underbarextradescender5000;">
+        <mspace id="ref001" height="1em" width="3em" style="background: green"/>
+        <munder style="background: cyan" id="el0011">
+          <mspace id="base0011" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0011" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munder style="background: cyan" id="el0012" accentunder="true">
+          <mspace id="base0012" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0012" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munder style="background: cyan" id="el0013" accentunder="true">
+          <mspace id="base0013" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0013" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover style="background: cyan" id="el0014">
+          <mspace id="base0014" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0014" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0014" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0015" accent="true">
+          <mspace id="base0015" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0015" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0015" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0016" accent="true">
+          <mspace id="base0016" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0016" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0016" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000underbarverticalgap7000;">
+        <mspace id="ref002" height="1em" width="3em" style="background: green"/>
+        <munder style="background: cyan" id="el0021">
+          <mspace id="base0021" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0021" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munder style="background: cyan" id="el0022" accentunder="true">
+          <mspace id="base0022" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0022" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munder style="background: cyan" id="el0023" accentunder="true">
+          <mspace id="base0023" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0023" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover style="background: cyan" id="el0024">
+          <mspace id="base0024" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0024" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0024" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0025" accent="true">
+          <mspace id="base0025" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0025" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0025" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0026" accent="true">
+          <mspace id="base0026" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0026" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0026" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000overbarextraascender3000;">
+        <mspace id="ref003" height="1em" width="3em" style="background: green"/>
+        <mover style="background: cyan" id="el0031">
+          <mspace id="base0031" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0031" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <mover style="background: cyan" id="el0032" accent="true">
+          <mspace id="base0032" height="5em" width="1em" style="background: black"/>
+          <mspace id="over0032" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <mover style="background: cyan" id="el0033" accent="true">
+          <mspace id="base0033" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0033" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <munderover style="background: cyan" id="el0034">
+          <mspace id="base0034" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0034" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0034" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0035" accent="true">
+          <mspace id="base0035" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0035" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0035" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0036" accent="true">
+          <mspace id="base0036" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0036" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0036" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000overbarverticalgap11000;">
+        <mspace id="ref004" height="1em" width="3em" style="background: green"/>
+        <mover style="background: cyan" id="el0041">
+          <mspace id="base0041" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0041" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <mover style="background: cyan" id="el0042" accent="true">
+          <mspace id="base0042" height="5em" width="1em" style="background: black"/>
+          <mspace id="over0042" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <mover style="background: cyan" id="el0043" accent="true">
+          <mspace id="base0043" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0043" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <munderover style="background: cyan" id="el0044">
+          <mspace id="base0044" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0044" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0044" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0045" accent="true">
+          <mspace id="base0045" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0045" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0045" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0046" accent="true">
+          <mspace id="base0046" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0046" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0046" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000underbarverticalgap7000;">
+        <mspace id="ref005" height="1em" width="3em" style="background: green"/>
+        <munder style="background: cyan" id="el0051">
+          <mspace id="base0051" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0051" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munder style="background: cyan" id="el0052" accentunder="true">
+          <mspace id="base0052" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0052" height="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover style="background: cyan" id="el0053">
+          <mspace id="base0053" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0053" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0053" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0054" accentunder="true">
+          <mspace id="base0054" height="5em" width="1em" style="background: black"/>
+          <mspace id="under0054" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0054" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000overbarverticalgap11000;">
+        <mspace id="ref006" height="1em" width="3em" style="background: green"/>
+        <mover style="background: cyan" id="el0061">
+          <mspace id="base0061" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0061" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <mover style="background: cyan" id="el0062" accent="true">
+          <mspace id="base0062" height="3em" width="1em" style="background: black"/>
+          <mspace id="over0062" height="1em" width="3em" style="background: red"/>
+        </mover>
+        <munderover style="background: cyan" id="el0063">
+          <mspace id="base0063" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0063" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0063" height="1em" width="3em" style="background: red"/>
+        </munderover>
+        <munderover style="background: cyan" id="el0064" accent="true">
+          <mspace id="base0064" height="3em" width="1em" style="background: black"/>
+          <mspace id="under0064" height="1em" width="3em" style="background: blue"/>
+          <mspace id="over0064" height="1em" width="3em" style="background: red"/>
+        </munderover>
+      </math>
+    </p>
+
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-4.tentative.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-4.tentative.html
new file mode 100644
index 0000000000..5000d24f18
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-4.tentative.html
@@ -0,0 +1,335 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<link rel="help" href="https://www.w3.org/TR/MathML3/chapter3.html#presm.mo.attrs">
+<meta name="assert" content="Elements munder, mover, munderover correctly use underbar/overbar and AccentBaseHeight parameters from the MATH table ; interaction with MathML3 mo@accent.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: accentbaseheight4000underbarextradescender5000;
+    src: url("/fonts/math/underover-accentbaseheight4000-underbarextradescender5000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000underbarverticalgap7000;
+    src: url("/fonts/math/underover-accentbaseheight4000-underbarverticalgap7000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000overbarextraascender3000;
+    src: url("/fonts/math/underover-accentbaseheight4000-overbarextraascender3000.woff");
+  }
+  @font-face {
+    font-family: accentbaseheight4000overbarverticalgap11000;
+    src: url("/fonts/math/underover-accentbaseheight4000-overbarverticalgap11000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 2;
+  var axisBaseHeight = 4000 *  emToPx;
+  var shortBaseHeight = 3000 * emToPx; // shortBaseHeight < axisBaseHeight
+  var tallBaseHeight = 5000 * emToPx; // tallBaseHeight > axisBaseHeight
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 1; i <= 4; i++) {
+        for (var j = 1; j <= 6; j++) {
+           var baseId = ("base00" + i) + j;
+           assert_approx_equals(getBox("ref00" + i).bottom,
+                                getBox(baseId).bottom,
+                                epsilon,
+                                "alignment of " + baseId);
+        }
+      }
+    }, "Baseline alignment");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      for (var i = 1; i <= 4; i++) {
+        for (var j = 1; j <= 6; j++) {
+           var baseId = ("base00" + i) + j;
+           assert_approx_equals(getBox(baseId).height,
+                                j == 2 || j == 5 ?
+                                tallBaseHeight :shortBaseHeight,
+                                epsilon,
+                                "height of " + baseId);
+        }
+      }
+    }, "Heights of bases");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0014").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0015").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref001").bottom - getBox("over0016").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el001" + j;
+        var baseId = "base001" + j;
+        var underId = "under001" + j;
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             0, epsilon,
+                             "gap between " + baseId + " and " + underId);
+        assert_approx_equals(getBox(elId).bottom - getBox(underId).bottom,
+                             v, epsilon,
+                             "extra descender below " + underId);
+      }
+    }, "AccentBaseHeight, UnderbarExtraDescender");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0024").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0025").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref002").bottom - getBox("over0026").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el002" + j;
+        var baseId = "base002" + j;
+        var underId = "under002" + j;
+        var gap = (j == 2 || j == 3 ? 0 : v);
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             gap, epsilon,
+                             "gap between " + baseId + " and " + underId);
+      }
+    }, "AccentBaseHeight, UnderbarVerticalGap");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0031").bottom,
+                           shortBaseHeight, epsilon,
+                           "mover: nonaccent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0032").bottom,
+                           tallBaseHeight, epsilon,
+                           "mover: accent over tall base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0033").bottom,
+                           axisBaseHeight, epsilon,
+                           "mover: accent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0034").bottom,
+                           shortBaseHeight, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0035").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref003").bottom - getBox("over0036").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 1; j <= 6; j++) {
+        var elId = "el003" + j;
+        var baseId = "base003" + j;
+        if (j >= 4) {
+          var underId = "under003" + j;
+          assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                               0, epsilon,
+                               "gap between " + baseId + " and " + underId);
+        }
+        var overId = "over003" + j;
+        assert_approx_equals(getBox(overId).top - getBox(elId).top,
+                             v, epsilon,
+                             "extra ascender below " + overId);
+      }
+    }, "AccentBaseHeight, OverbarExtraAscender");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      v = 11000 * emToPx;
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0041").bottom,
+                           shortBaseHeight + v, epsilon,
+                           "mover: nonaccent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0042").bottom,
+                           tallBaseHeight, epsilon,
+                           "mover: accent over tall base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0043").bottom,
+                           axisBaseHeight, epsilon,
+                           "mover: accent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0044").bottom,
+                           shortBaseHeight + v, epsilon,
+                           "munderover: nonaccent over short base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0045").bottom,
+                           tallBaseHeight, epsilon,
+                           "munderover: accent over tall base");
+      assert_approx_equals(getBox("ref004").bottom - getBox("over0046").bottom,
+                           axisBaseHeight, epsilon,
+                           "munderover: accent over short base");
+      for (var j = 4; j <= 6; j++) {
+        var baseId = "base004" + j;
+        var underId = "under004" + j;
+        assert_approx_equals(getBox(underId).top - getBox(baseId).bottom,
+                             0, epsilon,
+                             "gap between " + baseId + " and " + underId);
+      }
+    }, "AccentBaseHeight, OverbarVerticalGap");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: accentbaseheight4000underbarextradescender5000;">
+        <mspace id="ref001" height="1em" width="3em" style="background: green"/>
+        <munder style="background: cyan" id="el0011">
+          <mspace id="base0011" height="3em" width="1em" style="background: black"/>
+          <mo id="under0011" style="color: blue">&#xB0;</mo>
+        </munder>
+        <munder style="background: cyan" id="el0012">
+          <mspace id="base0012" height="5em" width="1em" style="background: black"/>
+          <mo id="under0012" style="color: blue">&#x2D8;</mo>
+        </munder>
+        <munder style="background: cyan" id="el0013">
+          <mspace id="base0013" height="3em" width="1em" style="background: black"/>
+          <mo id="under0013" style="color: blue">&#x2D8;</mo>
+        </munder>
+        <munderover style="background: cyan" id="el0014">
+          <mspace id="base0014" height="3em" width="1em" style="background: black"/>
+          <mo id="under0014" style="color: blue">&#xB0;</mo>
+          <mo id="over0014" style="color: red">&#xB0;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0015" accent="true">
+          <mspace id="base0015" height="5em" width="1em" style="background: black"/>
+          <mo id="under0015" style="color: blue">&#x2D8;</mo>
+          <mo id="over0015" style="color: red">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0016" accent="true">
+          <mspace id="base0016" height="3em" width="1em" style="background: black"/>
+          <mo id="under0016" style="color: blue">&#x2D8;</mo>
+          <mo id="over0016" style="color: red">&#x2D8;</mo>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000underbarverticalgap7000;">
+        <mspace id="ref002" height="1em" width="3em" style="background: green"/>
+        <munder style="background: cyan" id="el0021" accentunder="false">
+          <mspace id="base0021" height="3em" width="1em" style="background: black"/>
+          <mo id="under0021" style="color: blue">&#x2D8;</mo>
+        </munder>
+        <munder style="background: cyan" id="el0022">
+          <mspace id="base0022" height="5em" width="1em" style="background: black"/>
+          <mo id="under0022" style="color: blue" accent="true">&#x2D8;</mo>
+        </munder>
+        <munder style="background: cyan" id="el0023">
+          <mspace id="base0023" height="3em" width="1em" style="background: black"/>
+          <mo id="under0023" style="color: blue" accent="true">&#xB0;</mo>
+        </munder>
+        <munderover style="background: cyan" id="el0024">
+          <mspace id="base0024" height="3em" width="1em" style="background: black"/>
+          <mo id="under0024" style="color: blue" accent="false">&#x2D8;</mo>
+          <mo id="over0024" style="color: red" accent="false">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0025">
+          <mspace id="base0025" height="5em" width="1em" style="background: black"/>
+          <mo id="under0025" style="color: blue" accent="false">&#x2D8;</mo>
+          <mo id="over0025" style="color: red">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0026">
+          <mspace id="base0026" height="3em" width="1em" style="background: black"/>
+          <mo id="under0026" style="color: blue" accent="false">&#x2D8;</mo>
+          <mo id="over0026" style="color: red">&#x2D8;</mo>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000overbarextraascender3000;">
+        <mspace id="ref003" height="1em" width="3em" style="background: green"/>
+        <mover style="background: cyan" id="el0031">
+          <mspace id="base0031" height="3em" width="1em" style="background: black"/>
+          <mo id="over0031" style="color: red">&#xB0;</mo>
+        </mover>
+        <mover style="background: cyan" id="el0032" accent="true">
+          <mspace id="base0032" height="5em" width="1em" style="background: black"/>
+          <mo id="over0032" style="color: red">&#xB0;</mo>
+        </mover>
+        <mover style="background: cyan" id="el0033">
+          <mspace id="base0033" height="3em" width="1em" style="background: black"/>
+          <mo id="over0033" style="color: red">&#x2D8;</mo>
+        </mover>
+        <munderover style="background: cyan" id="el0034">
+          <mspace id="base0034" height="3em" width="1em" style="background: black"/>
+          <mo id="under0034" style="color: blue">&#xB0;</mo>
+          <mo id="over0034" style="color: red" accent="false">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0035" accent="true">
+          <mspace id="base0035" height="5em" width="1em" style="background: black"/>
+          <mo id="under0035" style="color: blue">&#x2D8;</mo>
+          <mo id="over0035" style="color: red">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0036" accent="true">
+          <mspace id="base0036" height="3em" width="1em" style="background: black"/>
+          <mo id="under0036" style="color: blue">&#x2D8;</mo>
+          <mo id="over0036" style="color: red">&#x2D8;</mo>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: accentbaseheight4000overbarverticalgap11000;">
+        <mspace id="ref004" height="1em" width="3em" style="background: green"/>
+        <mover style="background: cyan" id="el0041">
+          <mspace id="base0041" height="3em" width="1em" style="background: black"/>
+          <mo id="over0041" style="color: red">&#xB0;</mo>
+        </mover>
+        <mover style="background: cyan" id="el0042" accent="true">
+          <mspace id="base0042" height="5em" width="1em" style="background: black"/>
+          <mo id="over0042" style="color: red">&#xB0;</mo>
+        </mover>
+        <mover style="background: cyan" id="el0043">
+          <mspace id="base0043" height="3em" width="1em" style="background: black"/>
+          <mo id="over0043" style="color: red">&#x2D8;</mo>
+        </mover>
+        <munderover style="background: cyan" id="el0044">
+          <mspace id="base0044" height="3em" width="1em" style="background: black"/>
+          <mo id="under0044" style="color: blue">&#xB0;</mo>
+          <mo id="over0044" style="color: red" accent="false">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0045" accent="true">
+          <mspace id="base0045" height="5em" width="1em" style="background: black"/>
+          <mo id="under0045" style="color: blue">&#x2D8;</mo>
+          <mo id="over0045" style="color: red">&#x2D8;</mo>
+        </munderover>
+        <munderover style="background: cyan" id="el0046" accent="true">
+          <mspace id="base0046" height="3em" width="1em" style="background: black"/>
+          <mo id="under0046" style="color: blue">&#x2D8;</mo>
+          <mo id="over0046" style="color: red">&#x2D8;</mo>
+        </munderover>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-1.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-1.html
new file mode 100644
index 0000000000..1c236eabed
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-1.html
@@ -0,0 +1,151 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters (embellished operators)</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover (with an embelished operator base) correctly use the limit parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: lowerlimitbaselinedropmin3000;
+    src: url("/fonts/math/limits-lowerlimitbaselinedropmin3000.woff");
+  }
+  @font-face {
+    font-family: lowerlimitgapmin11000;
+    src: url("/fonts/math/limits-lowerlimitgapmin11000.woff");
+  }
+  @font-face {
+    font-family: upperlimitbaselinerisemin5000;
+    src: url("/fonts/math/limits-upperlimitbaselinerisemin5000.woff");
+  }
+  @font-face {
+    font-family: upperlimitgapmin7000;
+    src: url("/fonts/math/limits-upperlimitgapmin7000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("under00011").top - getBox("ref0001").bottom,
+                           v, epsilon, "munder: under shift");
+      assert_approx_equals(getBox("under00012").top - getBox("ref0001").bottom,
+                           v, epsilon, "munderover: under shift");
+    }, "LowerLimitBaselineDropMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 11000 * emToPx;
+      assert_approx_equals(getBox("under00021").top - getBox("ref0002").bottom,
+                           v, epsilon, "munder: under gap");
+      assert_approx_equals(getBox("under00022").top - getBox("ref0002").bottom,
+                           v, epsilon, "munderover: under gap");
+    }, "LowerLimitGapMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref0003").top - getBox("over00031").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0003").top - getBox("over00032").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "UpperLimitBaselineRiseMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref0004").top - getBox("over00041").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0004").top - getBox("over00042").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "UpperLimitGapMin");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: lowerlimitbaselinedropmin3000;">
+        <mspace id="ref0001" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="under00011" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="under00012" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: lowerlimitgapmin11000;">
+        <mspace id="ref0002" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="under00021" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="under00022" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: upperlimitbaselinerisemin5000;">
+        <mspace id="ref0003" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="over00031" height="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00032" height="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: upperlimitgapmin7000;">
+        <mspace id="ref0004" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace id="over00041" depth="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mrow><mrow><mo movablelimits="false">&#x2211;</mo></mrow></mrow>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00042" depth="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-2.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-2.html
new file mode 100644
index 0000000000..04a97786c4
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-parameters-and-embellished-operator-2.html
@@ -0,0 +1,151 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>Underscripts and Overscripts parameters (embellished operators)</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#underscripts-and-overscripts-munder-mover-munderover">
+<meta name="assert" content="Elements munder, mover, munderover (with an embelished operator base) correctly use the stretch stack parameters from the MATH table.">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/mathml/support/feature-detection.js"></script>
+<script src="/mathml/support/fonts.js"></script>
+<style>
+  math, mspace, mo {
+    font-size: 10px;
+  }
+  @font-face {
+    font-family: bottomshiftdown3000;
+    src: url("/fonts/math/stretchstack-bottomshiftdown3000.woff");
+  }
+  @font-face {
+    font-family: gapbelowmin11000;
+    src: url("/fonts/math/stretchstack-gapbelowmin11000.woff");
+  }
+  @font-face {
+    font-family: topshiftup5000;
+    src: url("/fonts/math/stretchstack-topshiftup5000.woff");
+  }
+  @font-face {
+    font-family: gapabovemin7000;
+    src: url("/fonts/math/stretchstack-gapabovemin7000.woff");
+  }
+</style>
+<script>
+  var emToPx = 10 / 1000; // font-size: 10px, font.em = 1000
+  var epsilon = 1;
+
+  function getBox(aId) {
+    return document.getElementById(aId).getBoundingClientRect();
+  }
+
+  setup({ explicit_done: true });
+  window.addEventListener("load", () => { loadAllFonts().then(runTests); });
+
+  function runTests() {
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 3000 * emToPx;
+      assert_approx_equals(getBox("under00011").top - getBox("ref0001").bottom,
+                           v, epsilon, "munder: under shift");
+      assert_approx_equals(getBox("under00012").top - getBox("ref0001").bottom,
+                           v, epsilon, "munderover: under shift");
+    }, "StretchStackBottomShiftDown");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 11000 * emToPx;
+      assert_approx_equals(getBox("under00021").top - getBox("ref0002").bottom,
+                           v, epsilon, "munder: under gap");
+      assert_approx_equals(getBox("under00022").top - getBox("ref0002").bottom,
+                           v, epsilon, "munderover: under gap");
+    }, "StretchStackGapBelowMin");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 5000 * emToPx;
+      assert_approx_equals(getBox("ref0003").top - getBox("over00031").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0003").top - getBox("over00032").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "StretchStackTopShiftUp");
+
+    test(function() {
+      assert_true(MathMLFeatureDetection.has_mspace());
+
+      var v = 7000 * emToPx;
+      assert_approx_equals(getBox("ref0004").top - getBox("over00041").bottom,
+                           v, epsilon, "mover: over shift");
+      assert_approx_equals(getBox("ref0004").top - getBox("over00042").bottom,
+                           v, epsilon, "munderover: over shift");
+    }, "StretchStackGapAboveMin");
+
+    done();
+  }
+</script>
+</head>
+<body>
+  <div id="log"></div>
+    <p>
+      <math style="font-family: bottomshiftdown3000;">
+        <mspace id="ref0001" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="under00011" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="under00012" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: gapbelowmin11000;">
+        <mspace id="ref0002" height="1em" width="3em" style="background: green"/>
+        <munder>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="under00021" depth="1em" width="3em" style="background: blue"/>
+        </munder>
+        <munderover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="under00022" depth="1em" width="3em" style="background: blue"/>
+          <mspace height="1em" width="3em" style="background: black"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: topshiftup5000;">
+        <mspace id="ref0003" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="over00031" height="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00032" height="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+    <hr/>
+    <p>
+      <math style="font-family: gapabovemin7000;">
+        <mspace id="ref0004" height="1em" width="3em" style="background: green"/>
+        <mover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace id="over00041" depth="1em" width="3em" style="background: blue"/>
+        </mover>
+        <munderover>
+          <mrow><mrow><mo>&#x2192;</mo></mrow></mrow>
+          <mspace height="1em" width="3em" style="background: black"/>
+          <mspace id="over00042" depth="1em" width="3em" style="background: blue"/>
+        </munderover>
+      </math>
+    </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001-ref.html
new file mode 100644
index 0000000000..89ac9c6324
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001-ref.html
@@ -0,0 +1,167 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator (reference)</title>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001.html
new file mode 100644
index 0000000000..6b0f99ec11
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-001.html
@@ -0,0 +1,270 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-algorithms">
+<link rel="help" href="https://w3c.github.io/mathml-core/#dfn-algorithm-for-stretching-operators-along-the-inline-axis">
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-of-operators">
+<link rel="match" href="underover-stretchy-001-ref.html"/>
+<meta name="assert" content="Verify visual rendering of padding/border/margin on an operator, stretchy along the inline axis.">
+<script src="/mathml/support/feature-detection.js"></script>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+  <!-- The red mspace elements below are expected to be covered by the green
+       stretchy mo elements. -->
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="198px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="98px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002-ref.html
new file mode 100644
index 0000000000..c12c74d654
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002-ref.html
@@ -0,0 +1,167 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator, embellished with two nested mrows (reference)</title>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002.html
new file mode 100644
index 0000000000..a1cfa20bb4
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-002.html
@@ -0,0 +1,272 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator, embellished with two nested mrows</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-algorithms">
+<link rel="help" href="https://w3c.github.io/mathml-core/#dfn-algorithm-for-stretching-operators-along-the-inline-axis">
+<link rel="help" href="https://w3c.github.io/mathml-core/#algorithm-for-stretching-operators-along-the-block-axis">
+<link rel="help" href="https://w3c.github.io/mathml-core/#embellished-operators">
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-of-operators">
+<link rel="match" href="underover-stretchy-002-ref.html"/>
+<meta name="assert" content="Verify visual rendering of padding/border/margin on an embellished operator, stretchy along the inline axis.">
+<script src="/mathml/support/feature-detection.js"></script>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+  <!-- The red mspace elements below are expected to be covered by the green
+       stretchy mo elements. -->
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+            <mrow><mrow><mo lspace="0" rspace="0" style="color: green;">⥚</mo></mrow></mrow>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="198px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="98px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003-ref.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003-ref.html
new file mode 100644
index 0000000000..02c7ce2efb
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003-ref.html
@@ -0,0 +1,167 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator, embellished with an munderover (reference)</title>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003.html b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003.html
new file mode 100644
index 0000000000..735fcab63e
--- /dev/null
+++ b/testing/web-platform/tests/mathml/presentation-markup/scripts/underover-stretchy-003.html
@@ -0,0 +1,272 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>Horizontal stretchy operator, embellished with an munderover</title>
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-algorithms">
+<link rel="help" href="https://w3c.github.io/mathml-core/#dfn-algorithm-for-stretching-operators-along-the-inline-axis">
+<link rel="help" href="https://w3c.github.io/mathml-core/#algorithm-for-stretching-operators-along-the-block-axis">
+<link rel="help" href="https://w3c.github.io/mathml-core/#embellished-operators">
+<link rel="help" href="https://w3c.github.io/mathml-core/#layout-of-operators">
+<link rel="match" href="underover-stretchy-003-ref.html"/>
+<meta name="assert" content="Verify visual rendering of padding/border/margin on an embellished operator, stretchy along the inline axis.">
+<script src="/mathml/support/feature-detection.js"></script>
+<style>
+  @font-face {
+    font-family: TestFont;
+    src: url("/fonts/math/stretchy.woff");
+  }
+  math, mo {
+    font-family: TestFont;
+    font-size: 50px;
+  }
+</style>
+<body>
+  <p>This test passes if you see green rectangles and no red.</p>
+  <!-- The red mspace elements below are expected to be covered by the green
+       stretchy mo elements. -->
+
+  <div style="position: absolute; left: 3em; top; 3em;
+              width: 1000px; height: 500px; background: lightgreen;">
+
+    <div style="position: absolute; top: 1px; left: 1px;">
+      <!-- stretchy base in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 251px;">
+      <!-- stretchy script in munder -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munder>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munder>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </munder>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 1px;">
+      <!-- stretchy base in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 101px; left: 251px;">
+      <!-- stretchy script in mover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </mover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <mover>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </mover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 1px;">
+      <!-- stretchy base in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 201px; left: 251px;">
+      <!-- stretchy underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 1px;">
+      <!-- stretchy overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 501px;">
+      <!-- stretchy base and underscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 151px; left: 501px;">
+      <!-- stretchy base and overscript in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 301px; left: 501px;">
+      <!-- stretchy scripts in munderover -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="200px" height="0px"/>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+            <munderover><mo lspace="0" rspace="0" style="color: green;">⥚</mo><mspace/><mspace/></munderover>
+          </munderover>
+        </math>
+      </div>
+    </div>
+
+    <div style="position: absolute; top: 1px; left: 751px;">
+      <!-- Only stretchy operators in munderover. The widest unstretched size
+           is used as the target size. -->
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mspace width="198px" height="48px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="198px" style="background: red; margin: 1px;"/>
+            <mspace width="198px" height="98px" style="background: red; margin: 1px;"/>
+          </munderover>
+        </math>
+      </div>
+      <div style="position: absolute; left: 0; top: 0;">
+        <math>
+          <munderover>
+            <mo lspace="0" rspace="0" style="font-size: 1em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 4em; color: green;">⥚</mo>
+            <mo lspace="0" rspace="0" style="font-size: 2em; color: green;">⥚</mo>
+          </munderover>
+        </math>
+      </div>
+    </div>
+  </div>
+  <script>
+    MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");
+    MathMLFeatureDetection.ensure_for_match_reftest("has_munderover");
+  </script>
+</body>
+</html>
-- 
cgit v1.2.3