Is it OK to use unknown HTML tags?

Question

Correct me if I\'m mistaken, but AFAIK, unknown HTML tags in markup (i.e. tags not defined in the HTML spec, like say, ) will eventually be treate

Answer 1

Generally not recommendable, e.g. IE wont apply css-styles to unknown tags.

All other browsers render unknown tags as inline-Elements (which causes problems with nesting).

I recommend you the following article: http://diveintohtml5.info/ There is a section about unknown tags.