4.2.5 Operands
Each machine instruction takes from 0 up to 4 operands. (See the appropriate data sheet of your target device for a full list of machine instructions.) These operands give information to the instruction on the data that should be used and the storage location for the instruction. Operands must be separated from mnemonics by one or more spaces or tabs.
Separate multiple operands with commas. If commas do not separate your operands, the assembler displays a warning and takes its best guess on the separation of the operands. For most instructions, an operand consists of a core general-purpose register, label, literal, or basereg+offset.