format-number of a value at or beyond 2^53 ran an unguarded
Double-to-Int conversion, a fatal trap reachable from user data; a
fraction picture beyond 15 places overflowed the scale conversion the
same way; and xsl:number value= beyond 2^53 trapped identically.
Digit extraction clamps fraction places to 15 (the 2^53 exactness
bound), pads back to the picture's minimum, renders out-of-range
integers through the exponent expander, and xsl:number falls back to
plain number rendering outside [1, 2^53). Sort-key rows always carry
one key per sort. Regression tests cover all three trap paths.
key() resolves its index against the current node's own document,
built lazily per document root, so keys work inside document() trees;
a node-set use expression indexes the matched node under every
member's string value; and key() results return in document order
regardless of lookup value order. Xalan baseline 187 -> 182.
Sort keys evaluate once per node with the node's own position, size,
variables, and bindings, so position()-based keys work, and NaN keys
order before numbers under data-type=number. Match patterns evaluate
over the matched node's own document, so templates match nodes loaded
through document(); the match cache keys include the document
identity. Xalan baseline 204 -> 187 (sort 18 -> 11, mdocs 14 -> 6).
apply-templates and for-each keep attribute and namespace nodes in
their selections; the context carries the non-tree current node with
its owner element backing the tree-only machinery, XPath evaluation
and current() start from it, match patterns select attribute nodes
through attribute identities in the match cache, the built-in rules
copy an attribute's or namespace's value as text, xsl:copy copies the
focused attribute or declaration itself, and an attribute result
arriving after element content is ignored (the XSLT recovery).
Sorting, for-each, and choose move to XSLTSorting.swift for the file
caps. Xalan baseline 352 -> 292 (axes 35 -> 16, copy 29 -> 16).
