When a search result arrives at the filtering engine it has two state flags; DOWNLOAD and DISPLAY. Initially the state flags are in an "undefined" state, and by applying various tests to each result, these flags can be set to DO and DON'T.
Note: As soon as both state flags are defined, i.e. set to either DO or DON'T, the filtering is aborted, and the application will proceed to DISPLAY and/or DOWNLOAD if the respective flags are set. Furthermore, each of the flags can be set only once (subsequent attempts to set them will be silently ignored), so the order in which you set up the rules is quite important.