Method: Register the uninstall hook on activation
Method: The uninstall hook for the pue option.
Filter Hook: Controls the slug used for an additional field filter. This should generally be unique or else unexpected results could be returned when users apply the filter.
Method: Constructor function. a.k.a. Let’s get this party started!
Method: Load the Plugin Update Engine
Method: Invalidate the cache.
Class: Generates additional field filters if appropriate.
Method: Sets up additional field filters, if possible.
Filter Hook: Controls whether a filter is created or not for a particular additional field.