+* Extensions can now return detailed error information via the API when
+ preventing user actions using 'getUserPermissionsErrors' and similar hooks
+ by using ApiMessage instances instead of strings for the $result value.
+* $wgAPIMaxLagThreshold was added to limit bot changes when databases lag
+ becomes too high.
+* Skins and extensions can now use FlexBox mixins (.flex-display(@display: flex)
+ and .flex(@grow: 1, @shrink: 1, @width: auto, @order: 1)) in Less to create
+ cross-browser-compatible FlexBox rules. Users will still need to add fallback
+ float rules or the like for compatibility with IE9- separately.