defconst is a special form in `C source code'.


Define SYMBOL as a constant variable.
This declares that neither programs nor users should ever change the
value. This constancy is not actually enforced by Emacs Lisp, but
SYMBOL is marked as a special variable so that it is never lexically

The `defconst' form always sets the value of SYMBOL to the result of
evalling INITVALUE. If SYMBOL is buffer-local, its default value is
what is set; buffer-local values are not affected. If SYMBOL has a
local binding, then this form sets the local binding's value.
However, you should normally not make local bindings for variables
defined with this form.

The optional DOCSTRING specifies the variable's documentation string.