The current implementation of MediaWiki:Sidebar supports a completely undocumented * {{msg}} syntax.
It works along the lines of: * header ** {{msgname}}
And ends up with a 'header' section with the parsed contents of MediaWiki:Msgname outputted into it.
This feature didn't exist in 1.16, was introduced but was seemingly completely broken in 1.17 and finally made to work in 1.18.
However I have a number of issues with it: Conceptually: * The concept makes little sense, it uses the {{}} template syntax, but actually takes a message from the MediaWiki namespace, and it of course doesn't support any real transclusion syntax Implementation: * The implementation is a mess, with successive {{msgname}} calls in the same header replacing rather than appending to, and using a mess of a setup where these blocks are actually put into a separate array which is array_merged into the real sidebar array at the end.
But mostly I have a problem with the fact that it's getting in my way. I'm currently trying to fix up the limitation in our skin system that only allows us to sanely have one type of navigation (the sidebar). With the implementation of a new navigation message parser that can handle varying formats of messages. However {{msgname}} is not something that can see be cleanly implemented in it.
I'd like to remove this feature from 1.18 before it ends up released and people actually start using this feature in production where we start having to deal with backcompat. Are there any objections to it being removed?