Function Reference
— Built-in Function: warning (template, ...)
— Built-in Function: warning (id, template, ...)

Format the optional arguments under the control of the template string template using the same rules as the printf family of functions (see Formatted Output) and print the resulting message on the stderr stream. The message is prefixed by the character string ‘warning: ’. You should use this function when you want to notify the user of an unusual condition, but only when it makes sense for your program to go on.

The optional message identifier allows users to enable or disable warnings tagged by id. The special identifier ‘"all"’ may be used to set the state of all warnings. — Built-in Function: warning ("on", id)
— Built-in Function: warning ("off", id)
— Built-in Function: warning ("error", id)
— Built-in Function: warning ("query", id)

Set or query the state of a particular warning using the identifier id. If the identifier is omitted, a value of ‘"all"’ is assumed. If you set the state of a warning to ‘"error"’, the warning named by id is handled as if it were an error instead.

See also: warning_ids