A piece of code may cause an error when you evaluate it. You can
designate the error message with the @error{} command.
The @error{} command is displayed as `error-->' in Info
and as `error-->' in the printed output.
Thus,
@lisp
(+ 23 'x)
@error{} Wrong type argument: integer-or-marker-p, x
@end lisp
produces
(+ 23 'x) error--> Wrong type argument: integer-or-marker-p, x
This indicates that the following error message is printed when you evaluate the expression:
Wrong type argument: integer-or-marker-p, x
Note that `error-->' itself is not part of the error message.