The GDS assembler and linker
An assembler statement may have as many as four fields. The general format of a statement is:
The label and comment fields are optional. The operator field may be an assembler directive or an assembly mnemonic. Some operators do not require an operand, e.g. cpl.
If present, a label must be the first field in a source statement and must be terminated by a colon (:). Multiple labels may appear on successive lines. For example:
The legal characters ...