Deadline regex change: define the acceptable boundary

Under a deadline, write down what the regex must accept and reject before editing it. Test at least one normal match, one near miss, empty input, and a long malformed string if the pattern touches untrusted data. Verify flags and whether a partial match is acceptable. Do not claim a broad validation guarantee from a quick pattern check; use a parser or domain-specific validator when the format requires one. Preserve the previous pattern so an unexpected regression can be traced.