<!DOCTYPE html>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<svg>
<text y="20">
foo
<tspan dx="50">baz</tspan>
</text>
</svg>
<script>
runAfterLayoutAndPaint(function() {
let text = document.querySelector('tspan').previousSibling;
text.textContent = text.textContent + "bar";
}, true);
</script>