NitrOS9 is a modern clone of the original OS-9 operating system used on the coco3. Both OS-9 and NitrOS9 have an EDIT command, a line-based text editor. As far as I know, EDIT works the same in both. Documentation for the EDIT command can be found in the OS-9 Editor/Assembler/Debugger Manual.
One characteristic of EDIT is that exiting the editor using the "Q" command (or its alias ESC) automatically saves your edits:
If input and/or output files were specified on the OS-9 command line when you started the editor, the text in buffer number one would be written to the initial output file, then the remainder of the initial input file would be copied to the output file. After the text has been copied, the editor will be terminated and control will return to the shell.
ibid. p. 1-16
That's great, but what if I've just made a mess of the file, such as an erroneous delete, and now I want to exit EDIT without saving the file? The only way I've found to do this is to turn off or reset the computer.
How can I exit EDIT without saving the file?