Update location of HashMap
Replace deprecated call to `find`
Embark on the 4th DOM revision

This style will use raw pointers to nodes stored in arenas. Strings
will likewise be interned. It also creates a "thin" DOM to go along
with the typical "fat" DOM. In a fat DOM, every element has a
reference to the document from which it came. A thin DOM pushes that
responsibility onto the programmer, at the benefit of reduced size.
Element children are ordered
Element children know their parent
Changing parent of element removes element from original parent
Elements can be renamed
Fat DOM elements belong to a document
Elements have attributes
Attributes know their element
Attributes can be reset
Attributes can be iterated
Fat DOM attributes belong to a document
All thin DOM nodes delegate equality to the raw layer
Show implementations can use attribute methods directly
Elements can have text children
Text knows its parent
Text can be changed
Fat DOM text nodes belong to a document
Elements can have comment children