We currently load a module `jquery.mw-jump` on all pages in MediaWiki core (via the `mediawiki.page.ready` module).
As part of T192623, I was going to merge the mw-jump code into `mediawiki.page.ready`, but then I realised, this is quite trivial logic and would actually be simpler, faster, and better for accessibility if it were done in pure CSS. See the Gerrit patches linked below for specifics.
##### Currently
MediaWiki core defines the following three messages:
```lang=json,name=i18n/en.json
"jumpto": "Jump to:",
"jumptonavigation": "navigation",
"jumptosearch": "search",
```
And the following JavaScript code:
```lang=js,name=mw-jump.js
$( '.mw-jump' ).on( 'focus blur', 'a', function ( e ) {
if ( e.type === 'blur' || e.type === 'focusout' ) {
$( this ).closest( '.mw-jump' ).css( { height: 0 } );
} else {
$( this ).closest( '.mw-jump' ).css( { height: 'auto' } );
}
} );
```
Neither the messages nor the JavaScript is actually used by MediaWiki core (the messages aren't output, and the script isn't triggered, by something from the OutputPage, Skin or SkinTemplate classes). Instead, the various skins that used to be part of core (Vector, MonoBook, ..), use the messages in their own repos, and also craft (similar) HTML that is compatible with this script, depending on the fact that core will queue the script as part of `mediawiki.page.ready`.
This is essentially left-over technical debt from the splitting of the skins.
##### Proposed
The Vector and MonoBook skins will use their own messages, and use their own HTML/CSS for these accessibility links.
Once that is done, we can deprecate the messages and modules; to be removed in the next major release.