Error message string or PEAR_Error object. The default message is unknown error if left blank.

Error code. It is recommended to use an error code for even the simplest errors, in order to simplify error handling and processing.

Error mode. This is one of PEAR_ERROR_RETURN, PEAR_ERROR_PRINT, PEAR_ERROR_TRIGGER, PEAR_ERROR_DIE, PEAR_ERROR_CALLBACK, or PEAR_ERROR_EXCEPTION. See setErrorHandling() for detailed information and examples of the meaning of these constants.

Error options. This depends on the value of $mode, and is documented in setErrorHandling().

Optional user information. This can be used to store any error-specific information, and has an unspecified format.

Error class name to use as the error object. The default error class is PEAR_Error. Use this parameter to specify another class to use, such as a custom class extending PEAR_Error

Use this parameter if you are using a custom class that does not accept an error message in its constructor. Never use this parameter without the $error_class parameter - it will not work.