Escaping.text and Escaping.attribute rebuilt a value that needed escaping one
character at a time: result += String(character) for every unescaped character,
plus the escaped form for each marker. Re-escaping a text node that holds a
single '&' rebuilt the whole value grapheme by grapheme, and the per-character
String construction and append dominated the serialize path for entity-bearing
content.
Copy each run between escapable characters in a single append and rewrite only
the markers. The no-escaping-needed fast path (return the value unchanged) is
untouched. The output is byte-identical: matching is per-Character so multibyte
graphemes copy whole, and the escaped forms are the same.
Measured serialize ~7% faster on the 20k-item generated corpus via a same-state
A/B (~3.0x to ~2.8x slower than libxml2). Verified by EscapingBulkCopyTests (a
per-character-oracle differential with multibyte cases), the Apache Xalan
gold-output and C14N canonicalization suites, the full suite, the WASM build,
and an adversarial review that included a 400k-input fuzz.
Mihaela Mihaljevic
1d4ec91922