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<html xmlns="http://www.w3.org/1999/xhtml" xmlns:math="http://www.w3.org/1998/Math/MathML"> <body onload="boom();"> <script> function boom() { document.getElementById("merror").appendChild(document.getElementById("s")); } </script> <math:merror id="merror"></math:merror> <span id="s" /> </body> </html>