Rarely heard of it from any of the popular web design / development sites (blogs, forums, info portals and so forth), there’s actually a neglectable implementation of the tag <comment> in both Internet Explorer Windows and Internet Explorer Mac.
You are <comment>not</comment> browsing on Internet Explorer.
notbrowsing on Internet Explorer.
In IE, comment tags are treated the same way as any native HTML comments are, text in between the tags are effectively ignored. However in other browsers such as Firefox, the comment tag is rendered as a normal one.
No more than a spice to amuse though, because rarely any hacking situations require the differentiation of both IE from other browsers.