A guy I work with told me about a function that an old IBM text editor had that he said was useful, and that is to create folds in the file after a search such that every line that is visible contains the search pattern(except possibly the first). All lines that do not contain the search pattern are folded up to the last occurence of the pattern or the top of the file. One use for such a function is to be able to make a quick and dirty api of a source file. For example, if working in Java, you could run the function using the pattern "public|protected|private" and ithe results would be that only the method headers would be visible (well, close enough).