AT&T 6300 Programmer's Manual page 303

INSTR
Function
Special Values
start
>
LEN(string) the returned value is 0
start < 1 or
start >255
'string' is null
'substring'
cannot be found
'substring' is
null and start
is specified
'substring' is
null and start
is omitted
an error is returned
(Illegal function call)
the returned value is 0
the returned value is 0
the returned value is 'start'
the returned value is
1
Example 10 XS =
U
ABCDEB"
20 VS=uB"
30 PRINT INSTR(XS,VS);INSTR(4,XS,VS)
RUN
26
Ok
Note: The position at which the match is found
is always evaluated from the beginning of the
original string, even if start is specified.
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