for potentially slow POST requests that need to be as atomic as possible.
* ResourceLoader now loads all scripts asynchronously. The top-queue and
startup modules are no longer synchronously loaded.
+* 'mediawiki.ui.button' styles are no longer unconditionally loaded on every
+ page. During the deprecation period, the styles will only be loaded on pages
+ which contain 'mw-ui-button' in their HTML. Starting in 1.28, the styles will
+ only be loaded if explicitly required.
==== External libraries ====
* Update es5-shim from v4.0.0 to v4.1.5.
* (T53283) load.php sometimes sends 304 response without full headers
* (T65198) Talk page tabs now have a "rel=discussion" attribute
* (T98841) {{msgnw:}} now preserves comments even when subst: is not used.
+* (T104142) $wgEmergencyContact and $wgPasswordSender now use their default
+ value if set to an empty string.
=== Action API changes in 1.26 ===
* New-style continuation is now the default for action=continue. Clients may