At release 1.03, WebEx has implemented most features defined by the HTML 3.0 standard, such as tables and flowing inline images. Moreover, WebEx has some extra features which are not standard HTML, but proprietary to this browser (i.e., other browsers will not understand them): Look at a list of Web Explorers proprietary html tags. One should note that WebEx has not implemented proprietary html extensions of other vendors, especially Netscape's frames. Also, at least at the versions I know, some advanced HTML3 stuff such as the mathematical formula stuff, had not been implemented (but I did not yet see any browser with this).