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+<!DOCTYPE html>
+<title>CSSOM View - scrollIntoView considers sideways-rl writing mode</title>
+<meta charset="utf-8">
+<link rel="author" title="Cathie Chen" href="mailto:cathiechen@igalia.com">
+<link rel="help" href="https://drafts.csswg.org/cssom-view/#dom-element-scrollintoview">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<style>
+.box {
+  float: left;
+  width: 200px;
+  height: 200px;
+}
+#scroller {
+  writing-mode: sideways-rl;
+  overflow: scroll;
+  width: 300px;
+  height: 300px;
+}
+#container{
+  width: 600px;
+  height: 600px;
+}
+#target {
+  background-color: #ff0;
+}
+</style>
+<body>
+<div id="scroller">
+  <div id="container">
+    <!--  ROW-1  -->
+    <div class="row">
+      <div class="box"></div>
+      <div class="box"></div>
+      <div class="box"></div>
+    </div>
+
+    <!--  ROW-2  -->
+    <div class="row">
+      <div class="box"></div>
+      <div class="box" id="target"></div>
+      <div class="box"></div>
+    </div>
+
+    <!--  ROW-3  -->
+    <div class="row">
+      <div class="box"></div>
+      <div class="box"></div>
+      <div class="box"></div>
+    </div>
+  </div>
+</div>
+
+<script>
+// In sideways-rl mode, X corresponds to the block axis and is oriented leftward.
+// Y corresponds to the inline axis and is oriented downward.
+// So the beginning edges are the top and right edges and the ending edges are the bottom and left edges.
+
+// According to the spec, x be min(0, max(x, element padding edge width - element scrolling area width)).
+// So x is nonpositive and decreases leftward.
+
+// This assumes that the horizontal scrollbar is on the bottom side and the vertical scrollbar is on the left side.
+
+var target = document.getElementById("target");
+var scroller = document.getElementById("scroller");
+var scrollbar_width = scroller.offsetWidth - scroller.clientWidth;
+
+var scroller_width = scroller.offsetWidth;
+var scroller_height = scroller.offsetHeight;
+var box_width = target.offsetWidth;
+var box_height = target.offsetHeight;
+
+var expectedX = {
+  blockStart: -box_width,
+  blockCenter: -((3*box_width - scroller_width)/2) - scrollbar_width/2,
+  blockEnd: -(2*box_width - scroller_width) - scrollbar_width,
+};
+
+var expectedY = {
+  inlineStart: box_height,
+  inlineCenter: ((3*box_height - scroller_height)/2) + (scrollbar_width/2),
+  inlineEnd: ((2*box_height) - scroller_height) + scrollbar_width,
+};
+
+[
+  [{block: "start", inline: "start"}, expectedX.blockStart, expectedY.inlineStart],
+  [{block: "start", inline: "center"}, expectedX.blockStart, expectedY.inlineCenter],
+  [{block: "start", inline: "end"}, expectedX.blockStart, expectedY.inlineEnd],
+  [{block: "center", inline: "start"}, expectedX.blockCenter, expectedY.inlineStart],
+  [{block: "center", inline: "center"}, expectedX.blockCenter, expectedY.inlineCenter],
+  [{block: "center", inline: "end"}, expectedX.blockCenter, expectedY.inlineEnd],
+  [{block: "end", inline: "start"}, expectedX.blockEnd, expectedY.inlineStart],
+  [{block: "end", inline: "center"}, expectedX.blockEnd, expectedY.inlineCenter],
+  [{block: "end", inline: "end"}, expectedX.blockEnd, expectedY.inlineEnd],
+].forEach(([input, expectedX, expectedY]) => {
+  test(() => {
+    scroller.scrollTo(0, 0);
+    target.scrollIntoView(input);
+    assert_approx_equals(scroller.scrollLeft, expectedX, 0.5, "scrollX");
+    assert_approx_equals(scroller.scrollTop, expectedY, 0.5, "scrollY");
+  }, `scrollIntoView(${JSON.stringify(input)})`);
+})
+
+</script>
+
+</body>
+</html>