The EagleFiler manual says that the search box can be used to find not only the contents of the records, but also their tags.
The manual gives an “apple -orange” example to demonstrate negative criteria. This example works when searching record content, but not when searching tags.
(I created two text records, one tagged “apple orange” and one tagged “apple banana”. Searching for “apple” finds both records. Searching for “apple -orange” finds no records.)
Are negative searches not enabled for tag searches?