ASCII-ART TREE DOCUMENTATION

Every node in the tree starts with the two characters "| ". Then follows a
multiple of two spaces to indicate the nesting depth. The root node has a
multiple of zero spaces, its children a multiple of one, et cetera. Nodes
can be recognized as follows:

 * Element nodes are represented by a "<", then the tag name, then "> (",
   then the element prefix, then ", ", then the element local name, then
   ", ", then the element namespace and then ")".
 * Attributes are given, in source order, on subsequent nodes, as if they
   were children of the element node. Attribute nodes have the attribute
   name, then an "=" sign, then the attribute value in double quotes (")
   followed by a space, then "(", then the attribute prefix, then ", ", then
   the attribute local name, then ", ", then the attribute namespace and
   then ")".
 * Text nodes are string, in double quotes. Newlines are not escaped.
 * Comments start with "<!-- ", then the data, then " -->".
 * PIs are XXX
 * DOCTYPEs are not represented in the tree.