<.composer_help>

The composer's keymap, behind a help icon. It replaces a one-line hint under the composer. That line could only ever carry the one fact it had room for, and it spent it on Enter, which is the thing people already guess. The bindings worth telling anyone about are the ones with nothing on screen to suggest them: `@` opens the mention menu, and the composer takes bold and italic. It lives here rather than in the host application so that the keys and their documentation sit in the same file as `buildKeymap`. A guide a room away from the bindings it describes goes stale the first time someone changes one. Only bindings that exist are listed. The composer's schema allows `code` and `link` marks, but nothing binds a key to either and there are no input rules, so they arrive by paste alone and claiming a shortcut for them would be a lie.