modifying-taxonomic-filter

name	modifying-taxonomic-filter
description	Guides safe modification of the TaxonomicFilter — PostHog's multi-tab picker for events, actions, properties, cohorts, and more. Front-loads the empirical product reality (what users actually pick and search for) so changes can be judged against real behavior, not architectural taste. Use when adding features, fixing bugs, or refactoring TaxonomicFilter.

Modifying the TaxonomicFilter

The TaxonomicFilter is the picker users hit to choose any "thing PostHog knows about" — events, properties, actions, cohorts, groups. It's the on-ramp into almost every analytics and replay configuration. Code lives in frontend/src/lib/components/TaxonomicFilter/.

The unbreakable rule: changes that demote items users actually pick are regressions, even with all tests passing. Read "Product reality" before deciding any change is safe. Ordering, promotion, or position-0 changes need explicit human sign-off — don't let an agent decide alone.

Product reality (last refreshed 2026-05-02, 90-day window)

Ratios from production telemetry. Re-run via references/refreshing-product-reality.md when older than ~3 months.

How users pick

• Top three rows carry ~80% of selections (position 0: ~56%, position 1: ~15%, position 2: ~8%). Demoting a popular item out of the top three is a real-user regression.
• ~34% selection rate. Two of every three opens close without a pick. p50 dwell ~7s, p90 ~53s — most opens are quick glances.
• Selection paths: ~65% via search, ~19% browsed-no-search, ~16% from recents, <1% from pinned items.

What users select

Source group type	Share
events	~40%
event_properties	~30%
person_properties	~14%
cohorts	~2%
email_addresses	~2%
actions	~2%
pageview_urls	~1%
everything else	<1%

What users search for (share of top-8 terms)

Term	Share
email	~29%
url	~22%
user	~12%
utm	~10%
page	~9%
path	~8%
current	~6%
country	~5%

email and url are over half the top-8. They're the entire reason PROMOTED_PROPERTIES_BY_SEARCH_TERM (in infiniteListLogic.ts) maps them to $email and $current_url at position 0. Touching promotion or ordering needs explicit human sign-off.

Empty searches

email, url, utm, path against cohorts, event_feature_flags, session_properties produce most empty-result events — users type the same canonical terms across every tab. Tab order, suggested-filters aggregation, and shortcut routing are how they get to the right answer.

Input mode

~93% typed, ~7% pasted. Both feed inputMode on taxonomic_filter_search_query.

Telemetry is a contract

Five events validate every change. Treat property shapes as a public API:

• taxonomic filter closed — dwellMs, hadSelection
• taxonomic filter item selected — sourceGroupType, wasFromRecents, wasFromPinnedList, wasQuickFilter, hadSearchInput, position, query
• taxonomic_filter_search_query — searchQuery, groupType, inputMode, pastedFraction
• taxonomic filter empty result — groupType, searchQuery
• taxonomic filter category dropdown opened — A/B variant

Adding properties: fine. Removing dead ones: fine. Renaming or repurposing silently is the worst case — dashboards keep working and start lying.

Variants you might not see locally

TAXONOMIC_FILTER_CATEGORY_DROPDOWN resolves to 'control' (tab pills) or 'pill' (suffix dropdown). Bug reports that don't reproduce locally are usually a variant mismatch. Touching tab rendering means testing both.

Pre-change checklist

• Read references when relevant: architecture, common-pitfalls (X/Y matrix), call-sites (smoke tests), testing-patterns
• Test both control and pill dropdown variants if you touched tabs
• Confirm telemetry payloads still have the same property shape
• Ordering / promotion / position-0 -> human sign-off, not agent judgement

hogli test frontend/src/lib/components/TaxonomicFilter/