You probably haven't heard of VTML - this is the language Allaire designed to allow for tag editors in HomeSite and Studio. It's also one of the least used features of HS, probably because not too many people create custom tags and share them with the world. VTML allowed you to design a nice tag editor so that a person could just enter, <cf_foo> into the editor, right click, and fill out the appropriate fields. Unfortunately, VTML was a real pain in the rear to use. This is not to say it's a bad feature, it was just difficult to use properly.
The reason I bring all of this up is because a company, Intelix, has designed a very simple, very easy to use online VTML builder. You can find it here:
http://www.smartsofttools.com/vtmlbuilder (FYI, this link is now dead since the site seems to have expired.)