Same-name xsl:attribute-set declarations merge as ordered definitions
per 7.1.4, each expanding its used sets before its own attributes with
later definitions winning; xsl:copy carries the source element's
in-scope namespace nodes per 7.5; the namespace fixup lets a carried
attribute prefix shadow an inherited binding unless the element's own
name relies on it; the html method minimizes boolean attributes whose
value repeats their name; and external DTDs and entities in the
stylesheet or source resolve through the transform's document loader.
Four unit tests pin the behaviors. Xalan baseline 174 -> 159
(attribset 13 -> 4, copy 12 -> 7).
Add the PureXML.HTML namespace: a lenient tokenizer for tag-soup input
(case-insensitive tags; quoted, unquoted, and boolean attributes; comments;
doctype; character references), a tree builder handling void elements,
optional end tags (li, p, table rows and cells), raw-text elements (script,
style), and unmatched end tags, and a serializer that writes void elements
unclosed and raw-text content unescaped.
Closes#36Closes#37Closes#38Closes#39Closes#20
