This is a simple interface which is implemented by a number of JSPWiki
components to signal that they should not be included in things like
module listings and so on. Because JSPWiki reuses its internal module
mechanisms for its own use as well (e.g. RenderingManager uses a PageFilter
to catch page saves), it's sort of dumb to have these all appear in the
"installed filters" list.
A plugin developer should never implement this interface.