Regex experiments without a deploy loop
Validation rules for invoice numbers, slugify filters, and log parsers all start as regex sketches. Iterating in-browser saves a commit-push-wait cycle and keeps PII-laden sample lines off shared CI logs.
Capture groups and replacements
Numbered groups ($1, $2) power rewrite pipelines. Verify group boundaries on empty matches and optional segments—off-by-one group indexes are a frequent source of silent data loss.
Cross-language porting
Before copying a working JS pattern into Java or Go, check Unicode class support and escaping rules. A green highlight here is necessary but not sufficient for backend compatibility.