The operation entry is the symbolic operation code specifying the machine, assembler, or macro instruction operation. The following rules apply to the operation entry:

• An operation entry is mandatory, and it must appear on the same line as any name entry.
• For machine and assembler instructions, it must be a valid symbol at assembly time (after substitution for variable symbols, if specified), consisting of 63 or fewer alphanumeric characters, the first which must be alphabetic. Most standard symbolic operation codes are five characters or fewer. For a description of machine instructions, refer to the z/Architecture Principles of Operation information. For a summary of assembler instructions, see Assembler instructions.

  The standard set of codes can be changed by OPSYN instructions (see OPSYN instruction).

• For macro instructions, the operation entry can be any valid symbol.
• An operation entry cannot be continued on the next statement.