From 43a97878ce14b72f0981164f87f2e35e14151312 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 11:22:09 +0200
Subject: Adding upstream version 110.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../snap-after-relayout/adding-only-snap-area.html |  55 ++++++++++
 .../adding-snap-area-while-snapped.html            |  66 +++++++++++
 .../changing-scroll-snap-align.html                | 121 +++++++++++++++++++++
 .../changing-scroll-snap-type-on-root-element.html |  95 ++++++++++++++++
 .../changing-scroll-snap-type.html                 |  96 ++++++++++++++++
 .../snap-after-relayout/move-current-target.html   | 116 ++++++++++++++++++++
 .../not-resnap-outside-proximity-threshold.html    |  66 +++++++++++
 .../snap-after-relayout/remove-current-target.html |  65 +++++++++++
 .../snap-after-relayout/resnap-to-focused.html     |  82 ++++++++++++++
 .../snap-to-different-targets.html                 |  92 ++++++++++++++++
 10 files changed, 854 insertions(+)
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-only-snap-area.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-snap-area-while-snapped.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-align.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type-on-root-element.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/move-current-target.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/remove-current-target.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/resnap-to-focused.html
 create mode 100644 testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/snap-to-different-targets.html

(limited to 'testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout')
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-only-snap-area.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-only-snap-area.html
new file mode 100644
index 0000000000..53141707bb
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-only-snap-area.html
@@ -0,0 +1,55 @@
+<!DOCTYPE html>
+<title>
+  Adding a new snap area when there are none should make the scroller snap to it.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 100px;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="target"></div>
+</div>
+
+<script>
+const target = document.getElementById("target");
+const scroller = document.getElementById("scroller");
+
+test(() => {
+  scroller.removeChild(target);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.appendChild(target);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Adding a new snap area when there are none should make the scroller snap to it.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-snap-area-while-snapped.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-snap-area-while-snapped.html
new file mode 100644
index 0000000000..d26359658f
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/adding-snap-area-while-snapped.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<title>
+  Adding a new snap area while already snapped should not make the scroller snap to it.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#initial-target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 100px;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+#other-target {
+  width: 300px;
+  height: 300px;
+  top: 300px;
+  left: 300px;
+  background-color: red;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="initial-target"></div>
+  <div id="other-target"></div>
+</div>
+
+<script>
+const initial_target = document.getElementById("initial-target");
+const other_target = document.getElementById("other-target");
+const scroller = document.getElementById("scroller");
+
+test(() => {
+  scroller.removeChild(other_target);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  scroller.appendChild(other_target);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Adding a new snap area while already snapped should not make the scroller snap to it.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-align.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-align.html
new file mode 100644
index 0000000000..3be68fe841
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-align.html
@@ -0,0 +1,121 @@
+<!DOCTYPE html>
+<title>
+  Updating the snap alignment of a snap container's content should make the snap
+  container resnap accordingly.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 200px;
+  width: 200px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#initial-target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 100px;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+#other-target {
+  width: 300px;
+  height: 300px;
+  top: 300px;
+  left: 300px;
+  background-color: red;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+
+.snap-area {
+  scroll-snap-align: start !important;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="initial-target"></div>
+  <div id="other-target"></div>
+</div>
+
+<script>
+const initial_target = document.getElementById("initial-target");
+const other_target = document.getElementById("other-target");
+const scroller = document.getElementById("scroller");
+
+function cleanup() {
+  initial_target.style.setProperty("scroll-snap-align", "start");
+  other_target.style.setProperty("scroll-snap-align", "start");
+  initial_target.removeAttribute("class");
+}
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  initial_target.style.setProperty("scroll-snap-align", "end");
+  // target.top + target.height - scroller.height
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 200);
+}, "Changing the current target's snap alignment should make the scroller"
++ " resnap to it even if another snap position is closer to the current offset");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  initial_target.style.setProperty("scroll-snap-align", "none");
+  assert_equals(scroller.scrollTop, 300);
+  assert_equals(scroller.scrollLeft, 300);
+}, "Removing the current target's snap alignment should make the scroller"
++ " resnap to a new snap area.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  initial_target.style.setProperty("scroll-snap-align", "none");
+  other_target.style.setProperty("scroll-snap-align", "none");
+
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  initial_target.style.setProperty("scroll-snap-align", "start");
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Changing an element snap alignment from none to start should make the"
++ "scroller resnap.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  initial_target.style.setProperty("scroll-snap-align", "none");
+  other_target.style.setProperty("scroll-snap-align", "none");
+
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  initial_target.classList.add("snap-area");
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Changing an element snap alignment from none to start by adding a class"
++ " should make the scroller resnap.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type-on-root-element.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type-on-root-element.html
new file mode 100644
index 0000000000..c86f39b9d6
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type-on-root-element.html
@@ -0,0 +1,95 @@
+<!DOCTYPE html>
+<html>
+<title>
+  Updating the scroll-snap-type of the root element should make it resnap accordingly.
+  This is another vairant of changing-scroll-snap-type.html for the root element.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+html {
+  overflow: hidden;
+  scroll-snap-type: none;
+}
+
+#y-target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 0;
+  background-color: green;
+  scroll-snap-align: start none;
+}
+
+#x-target {
+  width: 300px;
+  height: 300px;
+  top: 0;
+  left: 100px;
+  background-color: red;
+  scroll-snap-align: none start;
+}
+
+.area {
+  width: 1000vw;
+  height: 1000vh;
+}
+</style>
+
+<div class="area"></div>
+<div id="x-target"></div>
+<div id="y-target"></div>
+
+<script>
+const x_target = document.getElementById("x_target");
+const y_target = document.getElementById("y_target");
+const scroller = document.documentElement;
+
+function cleanup() {
+  scroller.style.setProperty("scroll-snap-type", "none");
+}
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "y mandatory");
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 0);
+}, "Changing the scroller's snap type to y should make it resnap on the y-axis.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "x mandatory");
+  assert_equals(scroller.scrollLeft, 100);
+  assert_equals(scroller.scrollTop, 0);
+}, "Changing the scroller's snap type to x should make it resnap on the x-axis.");
+
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "x mandatory");
+  assert_equals(scroller.scrollLeft, 100);
+  assert_equals(scroller.scrollTop, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "y mandatory");
+  assert_equals(scroller.scrollTop, 100);
+}, "Changing the scroller's snap type axis should make it resnap.");
+</script>
+</html>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type.html
new file mode 100644
index 0000000000..70774b3d40
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/changing-scroll-snap-type.html
@@ -0,0 +1,96 @@
+<!DOCTYPE html>
+<title>
+  Updating the scroll-snap-type of a snap container should make it resnap accordingly.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: none;
+}
+
+#y-target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 0;
+  background-color: green;
+  scroll-snap-align: start none;
+}
+
+#x-target {
+  width: 300px;
+  height: 300px;
+  top: 0;
+  left: 100px;
+  background-color: red;
+  scroll-snap-align: none start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="x-target"></div>
+  <div id="y-target"></div>
+</div>
+
+<script>
+const x_target = document.getElementById("x_target");
+const y_target = document.getElementById("y_target");
+const scroller = document.getElementById("scroller");
+
+function cleanup() {
+  scroller.style.setProperty("scroll-snap-type", "none");
+}
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "y mandatory");
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 0);
+}, "Changing the scroller's snap type to y should make it resnap on the y-axis.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "x mandatory");
+  assert_equals(scroller.scrollLeft, 100);
+  assert_equals(scroller.scrollTop, 0);
+}, "Changing the scroller's snap type to x should make it resnap on the x-axis.");
+
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "x mandatory");
+  assert_equals(scroller.scrollLeft, 100);
+  assert_equals(scroller.scrollTop, 0);
+
+  scroller.style.setProperty("scroll-snap-type", "y mandatory");
+  assert_equals(scroller.scrollTop, 100);
+}, "Changing the scroller's snap type axis should make it resnap.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/move-current-target.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/move-current-target.html
new file mode 100644
index 0000000000..ccadc884c5
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/move-current-target.html
@@ -0,0 +1,116 @@
+<!DOCTYPE html>
+<title>
+  Moving the current snap target should make the scroller resnap to it.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: relative;
+  margin: 0;
+}
+
+#block {
+  height: 100px;
+  width: 100px;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#initial-target {
+  width: 300px;
+  height: 300px;
+  left: 100px;
+  top: 0;
+  transform: none;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+#other-target {
+  width: 300px;
+  height: 300px;
+  left: 300px;
+  background-color: red;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div id="block"></div>
+  <div id="initial-target"></div>
+  <div id="other-target"></div>
+  <div class="area"></div>
+</div>
+
+<script>
+const initial_target = document.getElementById("initial-target");
+const other_target = document.getElementById("other-target");
+const block = document.getElementById("block");
+const scroller = document.getElementById("scroller");
+
+function cleanup() {
+  initial_target.style.setProperty("transform", "none");
+  initial_target.style.setProperty("top", "0");
+  block.style.setProperty("height", "100px");
+}
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  initial_target.style.setProperty("top", "300px");
+  assert_equals(scroller.scrollTop, 400);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Moving the current snap target should make the scroller resnap to it.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  block.style.setProperty("height", "200px");
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Changing the layout of other elements should be able to cause resnapping to \
+the target.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  initial_target.style.setProperty("transform", "translate(0,100px)");
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Transforming the current snap target should make the scroller resnap to it.");
+
+test(t => {
+  t.add_cleanup(cleanup);
+  initial_target.style.setProperty("top", "100px");
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 100);
+
+  initial_target.style.setProperty("transform", "translate(0,100px)");
+  initial_target.style.setProperty("top", "0");
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 100);
+}, "Applying two property changes that do not change the visual offset of the \
+target should not change the scroll offset.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html
new file mode 100644
index 0000000000..b2c5720efb
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/not-resnap-outside-proximity-threshold.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<title>
+  Not re-snap once after a scroll operation has finished without snapping
+  because the scroll destination was outside of the snap proximity threshold.
+</title>
+<!-- This test assumes that all major browsers' default scroll-snap proximity
+     thresholds are greater than 200px. -->
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1780154">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 600px;
+  width: 600px;
+  overflow: hidden;
+  scroll-snap-type: y proximity;
+}
+
+.snap {
+  width: 300px;
+  height: 300px;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div class="snap" style="top: 0px;"></div>
+  <div class="snap" style="top: 500px;"></div>
+</div>
+
+<script>
+test(() => {
+  // The initial snap position is at (0, 0).
+  assert_equals(scroller.scrollTop, 0);
+  assert_equals(scroller.scrollLeft, 0);
+
+  // Scroll to a position where it's outside of the scroll-snap proximity
+  // threshold, so that it won't trigger snapping.
+  scroller.scrollTo(0, 250);
+
+  assert_equals(scroller.scrollTop, 250);
+  assert_equals(scroller.scrollLeft, 0);
+
+  // Changing the initial snap target position, but still it's outside of the
+  // threshold.
+  document.querySelectorAll(".snap")[0].style.top = "10px";
+
+  // Not re-snap to the last snap point.
+  assert_equals(scroller.scrollTop, 250);
+  assert_equals(scroller.scrollLeft, 0);
+}, "Not re-snap once after a scroll operation has finished without snapping " +
+   "because the scroll destination was outside of the snap proximity threshold.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/remove-current-target.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/remove-current-target.html
new file mode 100644
index 0000000000..82bddf8074
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/remove-current-target.html
@@ -0,0 +1,65 @@
+<!DOCTYPE html>
+<title>
+  Removing the current snap target should make the scroller snap to a new target.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#initial-target {
+  width: 300px;
+  height: 300px;
+  top: 100px;
+  left: 100px;
+  background-color: red;
+  scroll-snap-align: start;
+}
+
+#other-target {
+  width: 300px;
+  height: 300px;
+  top: 300px;
+  left: 300px;
+  background-color: green;
+  scroll-snap-align: start;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="initial-target"></div>
+  <div id="other-target"></div>
+</div>
+
+<script>
+const initial_target = document.getElementById("initial-target");
+const other_target = document.getElementById("other-target");
+const scroller = document.getElementById("scroller");
+
+test(() => {
+  scroller.scrollTo(0,0);
+  assert_equals(scroller.scrollTop, 100);
+  assert_equals(scroller.scrollLeft, 100);
+
+  scroller.removeChild(initial_target);
+  assert_equals(scroller.scrollTop, 300);
+  assert_equals(scroller.scrollLeft, 300);
+}, "Removing the current snap target should make the scroller snap to a new target.");
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/resnap-to-focused.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/resnap-to-focused.html
new file mode 100644
index 0000000000..637c578a85
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/resnap-to-focused.html
@@ -0,0 +1,82 @@
+<!doctype html>
+<title>Resnap to focused element after relayout</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+
+#snapper {
+    counter-reset: child 0;
+    width: 200px;
+    scroll-snap-type: block mandatory;
+    overflow:hidden;
+    height: 100px;
+}
+.child {
+    width: 100px;
+    height: 100px;
+    background:red;
+    text-align: center;
+    box-sizing: border-box;
+    counter-increment: child;
+    float: left;
+}
+.child.f {
+    background: green;
+    scroll-snap-align: center;
+}
+.child::before {
+    content: counter(child);
+}
+
+</style>
+
+<link rel=author title="Tab Atkins-Bittner" href="https://www.xanthir.com/contact/">
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap">
+<!--
+When re-snapping after a layout change,
+if multiple elements were capable of being the snap target previously,
+and one of them is focused,
+you must resnap to the focused one.
+-->
+<div id=snapper>
+    <div class="child no-snap" tabindex=-1></div>
+    <div class=child></div>
+    <div class="child f" tabindex=-1></div>
+    <div class="child f" tabindex=-1></div>
+    <div class=child></div>
+    <div class=child></div>
+</div>
+
+<script>
+
+var container = document.querySelector("#snapper");
+var [one,two] = document.querySelectorAll(".child.f");
+var unsnappable = document.querySelector(".child.no-snap");
+
+async_test(t=>{
+    requestAnimationFrame(()=>{
+        testSnap(t, one, 3);
+        requestAnimationFrame(()=>{
+            testSnap(t, two, 4);
+            requestAnimationFrame(()=>{
+                testSnap(t, one, 3);
+                t.done();
+            });
+        });
+    });
+});
+
+function testSnap(t, child, expectedRow) {
+    t.step(()=>{
+        unsnappable.focus();
+        container.style.width = "200px";
+        var startingRow = container.scrollTop/100 + 1;
+        assert_equals(startingRow, 2, "Initially snapped to row 2");
+        child.focus();
+        container.style.width = "100px";
+        var endingRow = container.scrollTop/100 + 1;
+        assert_equals(endingRow, expectedRow, `After resize, should snap to row ${expectedRow}.`);
+    });
+}
+
+</script>
diff --git a/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/snap-to-different-targets.html b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/snap-to-different-targets.html
new file mode 100644
index 0000000000..7ad659d8a6
--- /dev/null
+++ b/testing/web-platform/tests/css/css-scroll-snap/snap-after-relayout/snap-to-different-targets.html
@@ -0,0 +1,92 @@
+<!DOCTYPE html>
+<title>
+  The scroller should try to resnap to targets for both axes if possible.
+</title>
+<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+div {
+  position: absolute;
+  margin: 0;
+}
+
+#scroller {
+  height: 500px;
+  width: 500px;
+  overflow: hidden;
+  scroll-snap-type: both mandatory;
+}
+
+#x-axis-target {
+  scroll-snap-align: none start;
+  background-color: blue;
+  width: 100px;
+  height: 100px;
+  top: 400px;
+  left: 200px;
+}
+
+#y-axis-target {
+  scroll-snap-align: start none;
+  background-color: green;
+  width: 100px;
+  height: 100px;
+  top: 200px;
+  left: 400px;
+}
+
+#far-x-axis-target {
+  scroll-snap-align: none start;
+  background-color: blue;
+  width: 100px;
+  height: 100px;
+  top: 1200px;
+  left: 300px;
+}
+
+#far-y-axis-target {
+  scroll-snap-align: start none;
+  background-color: green;
+  width: 100px;
+  height: 100px;
+  top: 300px;
+  left: 1200px;
+}
+
+.area {
+  width: 2000px;
+  height: 2000px;
+}
+</style>
+
+<div id="scroller">
+  <div class="area"></div>
+  <div id="x-axis-target"></div>
+  <div id="y-axis-target"></div>
+  <div id="far-x-axis-target"></div>
+  <div id="far-y-axis-target"></div>
+</div>
+
+<script>
+
+const x_target = document.getElementById("x-axis-target");
+const y_target = document.getElementById("y-axis-target");
+const scroller = document.getElementById("scroller");
+
+test(t => {
+  // The scroller should be snapped to the two closest points on first layout.
+  assert_equals(scroller.scrollTop, 200);
+  assert_equals(scroller.scrollLeft, 200);
+  x_target.style.setProperty("left", "1000px");
+  y_target.style.setProperty("top", "1000px");
+
+  // The style change makes it impossible for the scroller to snap to both
+  // targets, but at least one of the targets should be preserved. The scroller
+  // should then re-evaluate the snap point for the other axis.
+  const snapped_to_x = scroller.scrollLeft == 1000 && scroller.scrollTop == 300;
+  const snapped_to_y = scroller.scrollTop == 1000 && scroller.scrollLeft == 300;
+  assert_true(snapped_to_x || snapped_to_y);
+}, "Scroller should snap to at least one of the targets if unable to snap to\
+both after a layout change.");
+</script>
-- 
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