Custom tags… why not?

Question

I found a site with an guide to add custom tags to html, the same way people make ie work with the new HTML5 tags. I must admit I think it would be great to add my own tags,

Answer 1

Elements defined in HTML have known semantics. These can be understood by browsers (especially useful if they don't have CSS support), screen readers, search engines, and any other user agent and then expressed to the user.

Your own elements are meaningless.