Use setq rather than (set 'foo bar).

Use setq rather than (set 'foo bar).
Use push+nreverse rather than append.
(xml-node-name, xml-node-attributes, xml-node-children):
Use defsubst rather than macros.
(xml-parse-region): Handle a nil return value from xml-parse-tag.
(xml-parse-tag): Don't skip white space.  Return nil for a comment.
Concat the two strings surrounding a comment into a single string.