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

I think you'd want to use XSLT to transform your XML to valid HTML. If you introduce your own custom tag, you are no longer writing HTML, but probably XML or SGML.