Describes the known strictness of a filter.
Note that for filters where the strictness is not known, %GTK_FILTER_MATCH_SOME is always an acceptable value, even if a filter does match all or no items.
The filter matches all items, gtk_filter_match() will alays return %TRUE.
The filter does not match any item, gtk_filter_match() will always return %FALSE.
The filter matches some items, gtk_filter_match() may return %TRUE or %FALSE
Describes the known strictness of a filter.
Note that for filters where the strictness is not known, %GTK_FILTER_MATCH_SOME is always an acceptable value, even if a filter does match all or no items.