Any routine within a program that is entered as a result of some
error condition having been detected. The actions taken by such a routine will
be dependent upon the reliability requirements that the program is expected to
meet and upon the strategy for error analysis and recovery. A typical error
routine might simply produce an error message (i.e. a message that reports the
occurrence of an error) or it might attempt to diagnose the cause of the error
or attempt to recover so that normal operation can continue.