key(), id(), and EXSLT set:leading/set:trailing sorted their result with
sorted(by: Node.precedes). precedes recomputes both nodes' document-order keys
on every comparison, and each key walks the node to the root taking its index
among each parent's children, a linear scan of a wide parent. Over a wide flat
fan-out the sort was therefore quadratic. key() also deduplicated its matches
with matched.contains(where: ===), a linear membership scan, O(m^2) in the
match count. The EXSLT relative() used the cache-less documentOrder, rescanning
the parent per node.
Sort through sortedByDocumentOrder() (each key computed once behind a shared
sibling-index cache), deduplicate key()'s matches through a Set, and give
relative() a shared cache. The selected nodes, their document order, and the
deduplication are unchanged.
A key()-driven transform over a 20k-element document drops from ~1.15s to
~0.43s (~2.7x). The full suite, the Apache Xalan XSLT gold-output corpus, the
W3C XPath/XSLT/EXSLT tests, and the WASM build stay green; XSLTKeyIdOrderTests
pins key() dedup-and-order and id() document order.
Mihaela Mihaljevic
4552d24067