AT&T 6300 Programmer's Manual page 366

ON ERROR GOTO
Statement
It is recommended that the error trapping
routine execute an ON ERROR GOTO 0 if an
error is found for which there is no recovery
action. (In this case the standard error
message will be displayed and execution will
stop.) The RESUME statement resumes
execution after the error handling routine has
been entered (see the RESUME statement in
this chapter). If a GWBASIC error (or a user-
defined error) is found, during the execution of
an error trapping routine the associated error
message is displayed and execution terminates.
Note: Error trapping does not occur within the
error trapping routine.
Example
7-210
10 ON ERROR GOTO 1000
20 INPUT R
30 IF R = 0 THEN ERROR 300
100 IF ERR = 300 THEN PRINT uRADIUS
NEGATIVE OR ZERO"
110 IF ERL=30 THEN RESUME 20
120 ON ERROR GOTO 0