Install mmm-mode by entering the following commands in the terminal:
sudo apt update sudo apt install mmm-mode
Description:
Multiple Major Mode for Emacs
MMM Mode is a minor mode for Emacs that allows Multiple Major Modes (hence the name) to coexist in one buffer. It is particularly well-suited to editing embedded code, such as Mason server-side Perl, or HTML output in CGI scripts.
Homepage: http://mmm-mode.sourceforge.net/
Version: 0.5.4-3
Section: universe/editors