Ninetyd, you are a complete hero, thank you so much for clarifying. That gives me enough to sort out this patch and get the logic the right way round. 

I think this bug will help a bit with the four different situations (paid searching paid, paid searching free, free searching paid and free searching free, right?) but as it stands, allow_comment_search is itself dependent on allow_search_by. The supplementary bug is http://bugs.dwscoalition.org/show_bug.cgi?id=5185 

That's going to make user caps for "can search" and "can search comments" but maybe I want to also add "journal can be searched" and "comments can be searched in journal"? I will play with it once I've fixed the backwards logic.

So, four situations we're dealing with, have I got this right?

Journal |          |  P       |   F
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Viewer |  P      | J+C    |  J only 
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           | F       | J+C     | No
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