As reported in http://crbug.com/97970:
<a href="anything"><span style="visibility:hidden;">text here</span></a>
Expected: Text is invisible, but span still clickable
Actual: Text is invisible, span not clickable
In IE9 (Windows 7) and Firefox 7.0.1 (MacOS X 10.6) and Opera 11.51 (MacOS X 10.6), the text is invisible, but the underline renders and the link is still clickable.