Let's say, you are writing some documentation in
text-mode. Inside it, you need to write a piece of C code with proper indentation. You can switch to
c-mode, but then the rest of your text starts looking weird with colors and all, and this is very distracting (to me at least). But Emacs, as usual, has a solution to this problem.
Select a few blank lines (where you want to insert your code) within the text, and give the command
M-x narrow-to-region(the keyboard shortcut for this is
C-x n n). You will find yourself in a buffer with only the region you selected. Then you can enter
c-modeand write the code. When done, you can go back to your original full view by using the command
C-x n w) and switch back to whatever mode you were in (
text-modein this case).
I find this pretty useful.