Note taking software: referencing text to searchable keywords I'm looking for software for macs geared towards organizing and referencing the text in notes. I'm currently studying pathology and would like to be able to "tag" a topic/heading within my notes (not the entire note itself) with a keyword that is searchable. For example, if I have Rheumatoid Arthritis, I'd like to be able to highlight it, and tag it with  multiple keywords or hashtags such as "hypersensitivity reaction type IV" or "#hypersensitivityrxntypeIV" and be able to search those keywords and have any of those topics I've tagged show up in the results. Anyone have any suggestions?
You may be interested in using MaxQDA, they are just now preparing to release a mac version. Although it is a software geared towards textual analysis and qualitative researchers, it can tag pieces of text pretty much like you say you want to do.