Thanks, gentlemen, that's helpful.

The reason i was asking is because of a technique i'm researching called DTR, dynamic text replacement. see this link (if you fee llike it ofcourse...)

http://www.alistapart.com/articles/dynatext .  This is a technique for replacing static textual html tags, such as <h1> <h2> with a styled image, using the textual content as an input for the "image creator" php script. I was wondering if the styled Gif is simply layered on top of the <h1> , on the exact screen space, thus simply hiding it , and displaying only the gif to the user, while both actuallt co-exist after the browser parsing sequence is completed.

 Thanks! 

Amir