When we roll out the Categories filter on Event Metrics, we need to add a section to the Help doc explaining its uses and quirks. Some things to include:
- Categories are wiki-specific.
- Explain how and why the search includes talk page categories but will count only main page edits.
- Some metrics are not possible when Categories are used.
- Quirks of the Categories system and why searching for broader categories may yield fewer results.
- How you get no files uploaded results for Wikipedias when you use Categories without Participants as per T214744
- Categories without Participants also means no Wikidata results.