command-error-function is a variable defined in `C source code'.
Its value is

  • This variable may be risky if used as a file-local variable.

Function to output error messages.
Called with three arguments:
- the error data, a list of the form (SIGNALED-CONDITION . SIGNAL-DATA)
such as what `condition-case' would bind its variable to,
- the context (a string which normally goes at the start of the message),
- the Lisp function within which the error was signaled.