Content revised 21 October 2026.
A useful regex review tests the boundary cases, not just the examples that work. Keep the rule’s purpose visible so another person can maintain it.
Separate inclusion from exclusion
Write the intended population in plain language. Test one positive, one negative and one ambiguous example. Combining many alternatives can make the condition harder to understand than several clear rules.
Check literal characters
A period, question mark or plus sign may have special meaning. Escape it where a literal value is intended. Review anchors and grouping so an alternative does not accidentally apply outside the intended boundary.
Inspect the feature behaviour
Confirm supported syntax and full-versus-partial matching in the actual Analytics field. A pattern copied from another tool may not behave identically. Do not apply it to an important dataset without checking representative values.
Keep a review note
Store the pattern, purpose and test examples with the report definition. When URLs or naming conventions change, retest the rule. A correct pattern can become outdated even when nobody edits it.
Official guidance: Analytics regex reference.