Steps to replicate the issue (include links if applicable):
- Have an existing mwlib render server.
- install Collection extension and configure LocalSettings.php to use the mwlib render server. (using the $wgCollectionMWServeURL variable)
What happens?:
There is nowhere in the Book Creator to have the Book Creator use your render server.
What should have happened instead?:
I should see a button to have my book rendered by my render server, Like this:
I should not have to read through the code to have to discover an undocumented configuration variable that mysteriously enables the section. This variable should at least be documented so that people with pre-existing mwlib render servers can continue to use it after upgrading.
Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):
1.42.1
Other information (browser name/version, screenshots, etc.):
Patch attached. This is not an ideal solution, but it at least documents the variable, and fixes the UI if this variable is set to false. Should be applicable with git patch.

