The following documents comprise the MLC Web Style Guide for writers. Basically, MLC uses the Northwestern Publishing House Style Guide and Dictionary with additions specific to MLC.
The recommended way to use these guides is this way:
look to the MLC House Style Guide
look to the Northwestern Publishing House Dictionary for quick-look items
look to the Northwestern Publishing House Style Guide for additional items
use your judgement/look at other parts of the website/ask the MLC editor