Group @testable imports at the bottom, per public/rules-swift's swiftformat. A
behavior-preserving import-ordering reformat across 252 files (mostly tests).
--trailingclosures was deliberately not adopted (cosmetic, and swiftformat flags
it as caution-worthy).
A document() reference with a #fragment selects a subset of the loaded
document via XPointer; a node-set first argument unions the documents
named by each node's string value; and a relative URI is resolved against
a caller-supplied baseURI (the loader is wrapped so xsl:include/xsl:import
resolve the same way). Closes the XSLT function/output audit.
