<!DOCTYPE html> <html> <head> <!-- Default to invisible text --> <style type="text/css" media="screen, print"> .hidden { color: white; } .visible { color: black; } </style> </head> <body> <!-- Nest successive radicals and test that the horizontal bar of one of them is drawn. Because the comparison is for inequality with about:blank, at most one can be visible --> <math> <mrow> <msqrt class="hidden"> <mspace width="1em" height="1em" /> <msqrt class="hidden"> <mspace width="1em" height="1em" /> <msqrt class="hidden"> <mspace width="1em" height="1em" /> <msqrt class="hidden"> <mspace width="1em" height="1em" /> <msqrt class="hidden"> <mspace width="1em" height="1em" /> <msqrt class="visible"> <mspace width="1em" height="1em" /> <msqrt class="hidden"> <mspace width="20em" height="1em" /> </msqrt> </msqrt> </msqrt> </msqrt> </msqrt> </msqrt> </msqrt> </mrow> </math> <!-- Block out all but the horizontal bar of the visible radical --> <div style="position: absolute; top: 5px; left: 0px; width: 20em; height: 10em; background: white;"></div> </body> </html>