Used to return values from a text filter plugin's processing method.
The typical use case for a text filter plugin's processing method is to just apply some filtering to the given text, but for more advanced use cases, it may be necessary to also:
Declare asset libraries to be loaded. Declare cache tags that the filtered text depends upon, so when either of those cache tags is invalidated, the filtered text should also be invalidated. Declare cache context to vary by, e.g. 'language' to do lang