...{All} to ParentNode. Exposes createDocumentFragment and
createComment on Document. Stubs out the document.body setter.
Also adds ParentNode back :^).
LibWeb keeps growing and the Web namespace is filling up fast.
Let's put DOM stuff into Web::DOM, just like we already started doing
with SVG stuff in Web::SVG.
The more generic virtual variant is renamed to node_name() and now only
Element has tag_name(). This removes a huge amount of String ctor/dtor
churn in selector matching.
