custom-add-optioncustom-add-option is a compiled Lisp function in `
(custom-add-option SYMBOL OPTION)
To the variable SYMBOL add OPTION.
If SYMBOL's custom type is a hook, OPTION should be a hook member.
If SYMBOL's custom type is an alist, OPTION specifies a symbol
to offer to the user as a possible key in the alist.
For other custom types, this has no effect.