Asking this question because it's really hard to Google "emacs customize" and get to the feature.
From the defcustom
documentation:
You can specify variables using
defcustom
so that you and others can then use Emacs’scustomize
feature to set their values. (You cannot use customize to write function definitions; but you can writedefuns
in your .emacs file. Indeed, you can write any Lisp expression in your .emacs file.)The
customize
feature depends on thedefcustom
macro. Although you can usedefvar
orsetq
for variables that users set, the defcustom macro is designed for the job.
I haven't been able to figure out what "customize" is from this definition.
For completeness I am reading the projectile.el
source code where this is used (although I don't really expect the answer to depend on the package).