>The SYNTAX portion of the documentation says you can use >registers (1) - (15), however in the PARAMETERS section, >there's no mention of registers.
That is the approach taken by a large number of the services documented in the z/OS books, particularly the older services. For them, the parameters section describes the operand. The syntax shows how you code it. For newer services, there is often a "To code" part of the parameter description that would usually have this information too. Peter Relson z/OS Core Technology Design
