Manual:$wgJobClasses

Details
Maps jobs to their handling classes. Extensions can add to this to provide custom jobs. See for more information.

Since MediaWiki 1.30, it may now specify callback functions as an alternative to plain class names. This is intended for extensions that want control over the instantiation of their jobs, to allow for proper dependency injection.

Extensions
Extensions can add to this via the object in  :

The key must be unique and match what's specified in the job's constructor, and the value is the job class.