Regex Tester implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t4-184

Effect

Computation or source lookup only

Input and validation requirements

• Division-by-zero is not applicable to this instrument, but an unguarded global zero-length pattern can cause an infinite loop if the implementation does not advance after an empty match.
• Invalid patterns or flags must produce a defined error result rather than a match list.
• UTF-16 offsets can split surrogate pairs when u is absent; the UI must label offsets as UTF-16 code units or explicitly convert them.
• Regexes with catastrophic backtracking can cause severe latency or denial of service; execution limits or cancellation are needed.
• Global matching state can persist in lastIndex when a reusable RegExp object is used, causing surprising results unless lastIndex is reset or managed explicitly.
• The native iOS note is correct: ICU NSRegularExpression is not behaviorally identical to JavaScript RegExp and must not be presented as an equivalent engine.
• The honest label should also disclose that JavaScript engine versions and supported flags can differ, and that match indices and zero-length behavior depend on the selected API contract.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "pattern": "cat",
    "flags": "gi",
    "test_string": "Cat scat"
  },
  "expected_outputs": {
    "match_list": [
      {
        "text": "Cat",
        "start": 0,
        "end": 3,
        "groups": []
      },
      {
        "text": "cat",
        "start": 5,
        "end": 8,
        "groups": []
      }
    ],
    "capture_groups": [
      [],
      []
    ],
    "highlighted_match_spans": [
      [
        0,
        3
      ],
      [
        5,
        8
      ]
    ],
    "match_count": 2
  },
  "working": "1. UTF-16 positions in \"Cat scat\": C=0, a=1, t=2, space=3, s=4, c=5, a=6, t=7. 2. /cat/i matches \"Cat\" at start 0, exclusive end 0+3=3. 3. It also matches the final three characters of \"scat\": start 5, exclusive end 5+3=8. 4. Global matching returns 2 matches. 5. 2 matches × 0 capture groups gives capture arrays [], []."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json