Target branch: release-0.8.x

What

Remove \s* from the parseInstruction regex in lib/sax.js so that trailing whitespace inside a processing instruction is preserved instead of silently stripped.

Why

Per XML spec §2.6, PI data is everything between the mandatory separator whitespace after the target and the closing ?>. Trailing whitespace inside the PI boundary is content — there is no rule to strip it. Conforming parsers (sax-js, libexpat) preserve it.

This was already fixed on master/0.9.x as a side-effect of the large DOCTYPE rewrite in PR #498 (22k lines). This PR is the minimal, non-breaking backport for the maintained 0.8.x line.

How

parseInstruction builds a substring that already excludes ?>, so $ anchors immediately before it. The \s* before $ was greedily consuming any trailing whitespace from PI data before passing it to domBuilder.processingInstruction. Removing it — while keeping *? on the data group to minimise diff — is the complete fix.

// before
source.substring(start, end).match(/^<\?(\S*)\s*([\s\S]*?)\s*$/)
// after
source.substring(start, end).match(/^<\?(\S*)\s*([\s\S]*?)$/)

Five existing snapshots in test/xmltest/__snapshots__/not-wf.test.js.snap were updated: they captured the old buggy behaviour (trailing space stripped from XML-declaration-like PIs in the not-well-formed corpus). The updated snapshots reflect the now-correct output.

Scope

• nodeName: undefined — already fixed in current source (dom.js:1209), not touched
• XML declaration in childNodes — architectural, out of scope

Changes

Checklist

• npm test — 673 tests pass (671 baseline + 2 new)
• npm run lint — clean
• npm run format — clean
• No API surface change — no index.d.ts or readme.md update needed

Addresses the trailing-whitespace sub-issue from #42, backporting #498 behaviour to 0.8.x.