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To highlight lines that exceed more than 80 characters, we can colorize the extraneous characters.
Add to your
highlight OverLength ctermbg=darkred ctermfg=white guibg=#FFD9D9 augroup vimrc_autocmds autocmd! autocmd BufEnter,WinEnter * call matchadd('OverLength', '\%>80v.\+', -1) augroup END
Every line which is longer than 80 characters will result in: