ISO Pascal reference manual

PROGRAM fail(output);
BEGIN
END.
PROCEDURE test;
LABEL 10, 20;
BEGIN
10: writeln('label 10 identifies this statement');
END; (no statement labelled 20: 1
*ERROR 82 -- labels must be in the range 0..9999
The Pascal standard states that labels are distinguished by their apparent
numerical value and that this value must be in the range 0..9999.
PROGRAM fail(output);
LABEL 1, {ok}
BEGIN
10000; [wrong}
1: writeln('ok');
10000: writeln('bad');
END.
*ERROR 83 -- a label is required here
In Pascal a label must be an integer constant in the range 0..9999. This
message is issued when such a label is required but has not been found.
PROGRAM fail(output);
LABEL x; (x is not an integer constant}
BEGIN
GOTO x; (ditto}
x: writeln('here'); [and ditto}
END.
*ERROR 84 -- this case label has already been used in this CASE
statement
This message is issued when a constant is used to label a statement for a
second or subsequent time.
Appendix A
Pascal Issue I 73