Radio Shack TRS-80 PC-3 Owner's Manual page 135

number. When a numeric expression is used, it must evaluate to a valid line number, i.e., 1 to 999, or an ERROR 4 will occur.
EXAMPLES
10 GOSUB 100
20
END
100 PRINT "HELLO"
110 RETURN
When this program is run it prints the word 'HELLO' one time.