Fountain Mode is compatible with Emacs version 24.4 and later.
For Emacs versions older than 26.1, there is a bug in the
outline library. This will be automatically patched provided
fountain-patch-emacs-bugs is non-nil and Emacs is installed with its Elisp source files.
For Emacs versions older than 25.1, the
seq library will need to be installed; if you install using the Emacs package management system,
seq will be installed automatically.