As debugging aids, the compiler provides the user with debugging lines and a compile time switch for debugging lines.
Debugging lines
A debugging line is any line with a ’D’ in column 7 (the indicator area) of the line.Any debugging line that consists solely of spaces from margin A to margin R is considered the same as a blank line.
The content of a debugging line must be such that a syntactically correct program is formed with or without the debugging lines being considered as comment lines.
After all COPY statements have been processed, a debugging line will be treated as program text if it is preceded by a WITH DEBUGGING MODE clause. Otherwise, it is treated as a comment line. Successive debugging lines are allowed.
Debugging lines are only permitted in fixed format.
Compile time switch
The WITH DEBUGGING MODE clause specified in the SOURCE-COMPUTER paragraph serves as a compile time switch for the debugging lines.
If the WITH DEBUGGING MODE clause is specified, all following debugging lines are compiled as specified in the rules described above. If it is not specified, the debugging lines are treated as comment lines by the compiler.