1209603-1.html
<!DOCTYPE HTML>
<title>Testcase, bug 1209603</title>
<style>
p {
font-size: 2em;
/* ensure font-size dependency in the margin struct; this is also in
the UA style sheet, but repeated here for clarity */
margin: 1em 0;
}
</style>
<div style="font-size: 20px"><p id="a">Should be 40px font size.</p></div>
<script>
var a = document.getElementById("a");
// force computation of the margin struct on A (caching in rule tree)
getComputedStyle(a, "").marginTop;
</script>
<!-- will dynamically change font-size to 10px later;
also needs to be different from 20px now to avoid sibling-sharing -->
<div style="font-size: 30px"><p id="b">Should be 20px font size.</p></div>
<script>
// Note that A and B share rule nodes, and note that the margin struct
// has been conditionally (on font size) cached on their shared rule node.
var b = document.getElementById("b");
// force style context construction and computation of the font struct on
// B's parent
getComputedStyle(b.parentNode, "").fontSize;
// force style context construction (and computation of the color
// struct) on B, but not the margin struct or font struct
getComputedStyle(b, "").color;
// restyle B and flush
b.parentNode.style.fontSize = "10px";
getComputedStyle(b, "").marginTop;
// This flush will call CalcStyleDifference on B, which will find no
// cached font struct on the old context, but which will find a
// cached margin struct on the rule node.
</script>
