I cannot see a back button in the library panel ... is there a keyboard equivalent.
I am tagging resources ... trying to bring order into my counseling resources ... and keep clicking on existing tags accidentally. This then seems to replace my carefully crafted library filter with a basic mytag: filter ... 
I am sure that there is a reason for this functionality ... I would prefer that it adds to my filter rather than replaces it ... but my key point is having replaced my filter ... how do I get my filter back? cmd-Z does not seem to return my filter ... I do not know if undo has undone my most recent tag edit ... I cannot see my resources because my filter changed (did I mention that bit!
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It is probably really obvious ...
Thanks.