ISO dates

Pull every ISO date (YYYY-MM-DD) out of a log line. The shape is rigid: four digits, dash, two digits, dash, two digits. Counted repetition was built for this.

A regex checks shape, not meaning: 9999-99-99 has the right shape and would match. Validating that a date is REAL is a job for the surrounding code, not the pattern. Knowing where that line sits is part of mastering regex.