Invisible Text Searches
This is largely for outline modes such as the Koutliner. By default, character-by-character interactive search on {C-s} will search through invisible/hidden text, making the text temporarily visible until point moves past that hidden part. When a search match is selected, the surrounding text remains visible.
You can temporarily disable searching of hidden text by typing {M-s i} while in an incremental search. This key sequence toggles that setting and makes searches look only at visible text (or the reverse when invoked again). The setting lasts through the current interactive search only.