# 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.
