Reach full XSLT 1.0 key, numbering, and document parity:
- xsl:key declarations are compiled into an index over the source tree;
the key() function looks nodes up by key name and value.
- format-number() renders a number against a picture string (digit places,
decimal point, grouping, percent), Foundation-free.
- xsl:number generates the context node's position rendered as arabic,
alphabetic, or roman numerals.
- document() resolves an external source through an injected loader so the
transform never reaches the filesystem or network by default.
These hang off an XPath function-table injection mechanism: the evaluator
merges an engine-supplied FunctionTable, letting XSLT register current(),
key(), format-number(), and document() per evaluation.
Closes#63
Add the string functions (concat, starts-with, contains, substring-before,
substring-after, substring, string-length, normalize-space, translate), the
number functions (sum, floor, ceiling, round), and the node functions
(local-name, name, namespace-uri, id, lang), merged into the evaluation
library. All pure Swift, no Foundation: substring search is hand-rolled.
Without a DTD, id() matches an attribute named id or xml:id.
Closes#41
