C-x 4 c : clone-indirect-buffer-other-window

I keep learning new tricks in emacs. Today I was studying an overstuffed file, with two large classes, and I needed to navigate around both as I followed the code paths bouncing back and forth between them. I frequently use the "narrow-to-region" command (C-x n n) to temporarily clip the buffer to a single class or method of interest, because then jumping to the beginning/end of the buffer really takes me quickly to the beginning/end of the class, and searching is limited to the class, etc. But this time, I needed to narrow the buffer to two separate regions.

Enter today's interesting command: "clone-indirect-buffer-other-window", reached by C-x 4 c . All the "C-x 4" commands put things in a new window (which means a new region of the current "frame", where each frame gets a new OS-level window). This one makes an "indirect buffer" that's a mirror of the current one, but with a slightly different name (it gets a <2> tacked on to the end). Both buffers are looking at the same file, so any changes you make in one will also appear in the other. But you can narrow each one separately. So I was able to narrow to the first class in the main buffer, and narrow to the second class in the second buffer, and then search/study/explore as if they were two entirely different files. When you're done, just close the second buffer.