=== Summary
**Remove IE11 from basic support.**
(NOTE)
Current policy: <https://www.mediawiki.org/wiki/Compatibility#Browsers>
Affected components: **MediaWiki core, skins and extensions**. Wikimedia Foundation libraries like #Codex and #OOUI.
=== Motivation
Improve the user experience by making pages load slightly faster and use less bandwidth, because we'd send less CSS code down the wire.
Take away maintenance-burden of writing fallback CSS for newer CSS features not supported in IE11. The effort spent in writing workarounds and addressing specific browser code is a waste of our limited resources.
Unlock use of newer CSS features that do not have a fallback and thus cannot be safely used today.
=== Statistics
//Superset (Wikimedia Foundation login only)//
**2022:** “~0.1%, down from ~0.5% at the start of 2022, and ~1.0% at the start of 2021.” –T288287#8617086
**2023:** {T331463}
// analytics.wikimedia.org//
https://analytics.wikimedia.org/dashboards/browsers/#all-sites-by-browser/browser-family-and-major-hierarchical-view
==== Development abilities to gain without IE11
[[ https://caniuse.com/?compare=edge+12%2Cie+11&compareCats=CSS%2CHTML5%2CSVG | Full list at caniuse ]]. Excerpt:
- `display: flex`, removal of pre-standard Flexbox implementation (bytes and pain saved) and only standard syntax support
- `calc()` as CSS unit value allowed
- `@supports` feature queries able to be used unrestrictedly
- TTF/OTF web font support
Note that custom properties aka CSS vars are not only blocked by IE11, but it's with 0.51% globally according to caniuse, the biggest of the remainders (Edge 12-15)
=== Acceptance criteria
[ ] Update https://www.mediawiki.org/wiki/Compatibility#Browser_support_matrix to remove IE11 from Grade C
[ ] {T340172}
[ ] {T340173}