<html xmlns="http://www.w3.org/1999/xhtml" xmlns:m="http://www.w3.org/1998/Math/MathML"> <head> <script> function boom() { document.getElementById("td").contentEditable = "true"; document.execCommand("justifyfull", false, null); } </script> </head> <body onload="boom();"> <m:msubsup><td id="td"><m:mn/></td></m:msubsup> </body> </html>