Namespace handling todo list

[evilpie]

This might be incomplete, but I will try to collect what I find here. (To be updated)

• Should all non-HTML elements be unknown? #167 Don't treat SVG / MathML elements as always unknown (This might involve some kind of baseline list here as well)
• Whitespace versus colon as a namespace separator #146 The current way of specifying namespace:element is not acceptable
• I am not totally convinced that we should be using "the rules for parsing tokens in foreign content" in normalize element name at all.
• xlink:href isn't handled at all e.g., Also sanitize javascript: href on MathML and SVG anchor? #168
• Aggressively disallow/drop elements and attributes with unknown (non-html/svg/math) namespaces?

[mozfreddyb]

Let's track the issues individually and close this one out