Ideally, one would be able to search through the 'documentaries' format (categories can't be refined using 'formats' for some reason, or vice versa, and as such is difficult to further filter out documentaries in that manner). I guess A-Z is the closest it'd come to (an alphabetical) filter, but it's still severely limited, as the descriptions aren't taken into account and if what one is looking for doesn't start at the beginning of the title it would be impossible to find it... e.g. "The science of serotonin" (it would, as such, be much easier if one could simply search for 'serotonin' within the 'documentaries' format).