MCL ships with a few extra handlers which might be useful but are not in the default set of handlers. You may use any of those handlers by renaming or symlinking (recommended) the file/folder so that it doesn't start with two or more underscores.
These handlers might origin from a 3rd party or are rather individual and are not necessarily supported. They might not be "polished" and may require slight code changes for you to work. Hopefully you find some further documentation ;-)