fix(xml): accept the element names XML actually allows

[productdevbook]

fix(xml): accept the element names XML actually allows

writeXml turns a column heading into an element name and validated it
with

/^[A-Za-z_][\w.-]*(?::[A-Za-z_][\w.-]*)?$/

which is ASCII. XML 1.0 §2.3's NameStartChar runs from #xC0, so every
accented or non-Latin heading was refused:

writeXml([{ Şehir: "İzmir" }])
ParseError: Invalid XML name for element "Şehir": "Şehir"

Şehir, Ünvan, Größe, café, naïve, 名前, Ελλάδα,
Кириллица — all valid XML, all rejected. A spreadsheet whose columns
are not named in English could not be written to XML at all. Not
mangled, not escaped: the format was unavailable, and the error said the
name was invalid when it was the check that was.

Found while testing #563, where a Turkish sheet could go to CSV, TSV,
JSON, NDJSON, HTML and Markdown but not XML.

The productions, minus the colon

NameStartChar and NameChar verbatim, with : pulled out so a name
may carry one prefix rather than a colon wherever it likes — that is
QName from Namespaces in XML §4, and it is what the old regex was
reaching for too.

The u flag is not optional here: #x10000–#xEFFFF is above the BMP, and
without it the surrogate halves match separately.

Nothing new is accepted that XML forbids. A leading digit, a leading
hyphen or dot, a space, <, two colons, the empty string, and a leading
combining mark — NameChar but not NameStartChar — are still refused,
each with a test.

Checked

27 tests, 14 of which fail against the old regex and none of which is
a rejection case: the tests that say what stays refused pass either way,
which is the point of having them.

The reader was never the problem — parseXml reads any well-formed name
— and a non-ASCII name now round-trips through both.

pnpm test green — 10,622 tests, 236 files.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com

🤖 Generated with Claude Code