auto-fill will only break a line at a whitespace character. Usually this is what you want. However, I'm writing a major mode for editing data files (DNA sequences) that contain long lines of text with no spaces, and I want them to auto-fill at exactly 80 columns. How can I achieve this?
i.e., I want to use auto-fill (or similar) to fill this:
to this (using 20-character lines instead of 80 for a shorter example):
ACCATCGAAACTTTGAACGC AAGTTGCGCCTCAAGCCATT AGGTTGAGGGCACGTTTGCT TGGGTGTCATTCGTTATGTC