Thread:Talk:ResourceLoader/JavaScript Deprecations/insertTags/reply

It is deprecated not removed. The function is still there and used by:
 * MediaWiki core's default editing toolbar
 * Extension:Charinsert

Note that the actual insertTags function has in fact already been replaced in 1.18 with a call into the jquery.textSelection module; but it's kept available for internal API compatibility.

The direct callers are on the way (though not yet 100%) to being superseded by Extension:WikiEditor's editing & toolbar widgets, which have more tightly integrated (and more flexible) ways to list things to insert into your editor (ultimately using jquery.textSelection as the actual implementation).