regex-tools/docs/FLAVOUR_SUPPORT.md

Flavour support

Flavour	Syntax	Execution	Replacement	Captures	Trace	Analysis	Generated cases	Native offsets
ECMAScript	regexpp 4.12.2; explanations partial/feature-matrix tested	Current browser RegExp; conformance tested	Bounded ECMAScript GetSubstitution	Named/numbered; final repeated capture; no history	Unavailable	Experimental static heuristics + bounded native probes	Bounded normalized-AST sampling; actual-engine verified	UTF-16
PCRE2 10.47	Application lexical provider partial; compiler authoritative	Pinned 8-bit WASM; bounded/killable/conformance tested	Native bounded pcre2_substitute() loop	Native named/numbered records; no capture history	Bounded reported automatic callouts; derived movement labels	Unavailable; ECMAScript heuristics are never applied	Unavailable; structural syntax provider is partial	UTF-8 bytes
Python re	Application lexical provider partial; compiler authoritative	CPython 3.14.2 in self-hosted Pyodide 314.0.3	Native bounded re expansion	Native named/numbered spans; no capture history	Unavailable	Unavailable; ECMAScript heuristics are never applied	Unavailable; structural syntax provider is partial	Code points
Java java.util.regex	Application lexical provider partial; compiler authoritative	TeaVM 0.15.0 class library; bounded/killable; not OpenJDK	TeaVM single-digit $n; no ${name}	Native numbered ranges; lexical names; no history	Unavailable	Unavailable; ECMAScript heuristics are never applied	Unavailable; structural syntax provider is partial	UTF-16
PCRE	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable
Go regexp	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Planned bytes
Rust regex	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Unavailable	Planned bytes
.NET	Unavailable	Unavailable	Unavailable	Planned capture history	Unavailable	Unavailable	Unavailable	Planned UTF-16

ECMAScript tests cover its complete exposed flag matrix, internal indices, zero-length iteration, captures, lookbehind, backreferences, Unicode properties and bounded replacement.

PCRE2 tests cover g, i, m, s, x, U, J, mandatory UTF/UCP, branch-reset groups, recursion, \K, duplicate names, native substitution, astral byte/UTF-16 ranges, zero-length iteration, compile errors, match limits and result/output truncation. Trace tests cover reported automatic callouts, bounded mark copying, native stop at the complete-event cap, compile ranges, worker loading and browser rendering.

Python tests cover application-level g, CPython flags a, i, m, s and x, Python-only named-group/replacement syntax, native re substitution, astral code-point/UTF-16 normalization, zero-length iteration, compile errors, result limits, runtime identity and worker recovery.

Java tests cover application-level g, TeaVM Pattern flags, Java named-group syntax, TeaVM's native single-digit $n Matcher replacement, explicit rejection of unsupported ${name}, astral UTF-16 ranges, zero-length iteration, compile errors, result limits, module identity and worker recovery. The runtime and UI explicitly report that TeaVM 0.15.0 is not OpenJDK and does not implement OpenJDK Pattern.UNICODE_CHARACTER_CLASS; U is a compatibility request rather than an exact implementation of that flag.

ECMAScript static findings and generated-input timing observations are advisory. They describe only the selected ECMAScript 2025 pattern, browser runtime and bounded inputs; they are not proofs of safety or general complexity.

ECMAScript generated-case version 1 uses only a complete accepted normalized AST, an explicit deterministic seed and bounded sampling strategies. Every retained positive or negative label is confirmed by the actual selected browser engine. PCRE2, Python and Java generation are unavailable because their current lexical providers are intentionally partial; ECMAScript behavior is never relabelled as another flavour.

The PCRE2, Python and Java explanation providers deliberately do not invent full structural coverage. PCRE2 branch-reset numbering is omitted from the syntax tree, while actual capture numbers, names and ranges still come from the selected runtime result.

ECMAScript and PCRE2 support exact-request comparison for syntax acceptance, engine compilation, matches, captures and engine-native replacement. Results align by normalized UTF-16 ranges while retaining each native offset model. Timeout, cancellation, rejection and truncation are never presented as equivalent results.

Pattern formatting is available only for an exact accepted ECMAScript regexpp snapshot. It canonicalizes literal slashes and raw control/line-separator representations, then requires paired actual-engine and applicable exact-test validation before apply. PCRE2, Python and Java formatting is unavailable because those providers are deliberately partial; their syntax is never treated as ECMAScript.

Subject minimization accepts only the verified ECMAScript and PCRE2 paths. Python and Java selections are disabled rather than being minimized through a different flavour. Semantic comparison is likewise an explicit ECMAScript/PCRE2 operation; it is not a generic four-way equivalence checker.

PCRE2 is the only current code-generation target. The reviewed C17 generator is pinned to the PCRE2 10.47 8-bit API; other language generators remain unavailable until they pass equivalent escaping and named-toolchain gates.