- without xmlns
- lower-case tags (e.g. <x3d>)
- no-self closing tags
XHTML encoding
- with xmlns
- case-sensitive tags (e.g. <X3D>)
- self-closing tags
<html xmlns="http://www.w3.org/1999/xhtml">
Unified XHTML/HTML encoding
- with xmlns
- case-insensitive tags
- no-self closing tags