* (bug 34876) jquery.makeCollapsible has been improved in performance.
* Added ContentHandler facility to allow extensions to support other content than wikitext.
See docs/contenthandler.txt for details.
+* New feature was developed for showing high-DPI thumbnails for high-DPI mobile
+ and desktop displays (configurable with $wgResponsiveImages).
+* Added new backend to represent and store information about sites and site
+ specific configuration.
+* jQuery UI upgraded from 1.8.23 to 1.8.24.
=== Bug fixes in 1.21 ===
* (bug 40353) SpecialDoubleRedirect should support interwiki redirects.
* action=edit and action=parse now support contentmodel and contentformat parameters to control the interpretation of
page content; See docs/contenthandler.txt for details.
* (bug 35693) ApiQueryImageInfo now suppresses errors when unserializing metadata.
+* (bug 40111) Disable minor edit for page/section creation by API
=== Languages updated in 1.21 ===