user-error

user-error is a compiled Lisp function in `subr.el'.

(user-error FORMAT &rest ARGS)

Signal a pilot error, making error message by passing all args to `format'.
In Emacs, the convention is that error messages start with a capital
letter but *do not* end with a period. Please follow this convention
for the sake of consistency.
This is just like `error' except that `user-error's are expected to be the
result of an incorrect manipulation on the part of the user, rather than the
result of an actual problem.