Protecting a file from accidental changes
From Vim Tips Wiki
created 2003 · complexity basic · author zzapper · version 5.7
A common programmimg situation, you are comparing two versions of the same file. One is the "reference file" which you don't want to update. However they look so similar that you can get confused.
Solution: Set the master file to read only, and change its color scheme.
:set nomodifiable :colorscheme peachpuff
Non-modifiable is better than
:set ro as
nomodifiable won't even let you start changing stuff, whereas
:set ro will only warn you once.
You can permanently protect a file by setting a suitable modeline :help modeline.