The initial processing of a macro definition is called editing. In editing, the assembler checks the syntax of the instructions and converts the source statements to an edited version used throughout the remainder of the assembly. The edited version of the macro definition is used to generate assembler language statements when the macro is called by a macro instruction. This is why a macro must always be edited, and consequently be defined, before it can be called by a macro instruction.

^z/VSEReading edited macros (z/VSE only) describes how you can use a LIBRARY exit to allow High Level Assembler to read edited macros.