Broaden the serializer and writer options from the audit:
- attributeQuote selects single or double quotes; the active quote is
escaped in values (apostrophe as ' in single-quote mode).
- lineEnding controls the inserted newline (set to CRLF for \r\n output).
- xml:space=preserve suppresses pretty-print indentation for an element
and its subtree; xml:space=default re-enables it.
- Writer gains writeStartElementNS(prefix:localName:namespaceURI:) and
writeNamespace(prefix:uri:), so callers no longer hand-format prefixes
and xmlns attributes.
CDATA-vs-escape and entity re-escaping strategies are left as a
follow-up; the current escaping is the safe default.
Closes#91
Add includeXMLDeclaration, xmlVersion, encodingName, and standalone to
Emitting.Options, with a single shared xmlDeclaration computation consumed
by both the tree serializer and the incremental writer. Writer gains
writeStartDocument(). Defaults stay off so fragment output is unchanged.
Closes#34
Add PureXML.Emitting.Writer, the libxml2 xmlTextWriter model: emit a document
with writeStartElement/writeAttribute/writeString/writeEndElement and friends,
never building a tree. Escaping is extracted into a shared Emitting.Escaping
helper used by both the writer and the serializer, so compact writer output is
byte-identical to serializing the equivalent tree. Pretty mode indents element
children (forward-only, so prefer compact for mixed content). Closes#32.
Reimplemented from the libxml2 model; no upstream code copied. 6 tests; 90 total.
Reimplement the serializer as an explicit work-stack walk instead of recursion,
mirroring libxml2's xmlNodeDumpOutputInternal, so it is no longer the depth
bottleneck. Reimplemented in Swift; no upstream code copied.
Also fix a mixed-content correctness bug: formatting is now suppressed for any
element with text or CDATA children (previously only when ALL children were
text), so pretty-printing never injects whitespace around significant text.
Note surfaced while testing: the remaining depth ceiling is the recursive
Model.Node indirect enum (recursive ARC teardown overflows at extreme depth),
which is why the parser must cap nesting depth (next).
The serializer escaped only & < " in attribute values, so an attribute holding
tab, newline, or carriage return would not survive a spec-compliant parser's
attribute-value normalization. Match the libxml2 attribute escape table: emit
	 for the whitespace characters and > for >. Behavior derived
from the libxml2 analysis (xmlsave.c / xmlIO.c escape tables), reimplemented in
Swift; no upstream code copied.
Root Swift package mirroring PureYAML's structure, rules, and verification
gates. Includes the XML node model (Node, Element, Attribute, QualifiedName),
a working emitter (Serializer) with escaping and pretty/compact options, and
structural validation. The parser surface is stable; parse() raises
notImplemented until the scanner lands, pinned by a test.
- dependency-free, namespaced under PureXML
- portability and style gates carried over (style, namespacing, forbidden
patterns, swiftformat, swiftlint, linux, wasm, windows CI)
- 11 tests passing
