GEMS17 — Describe how directives can be used to access leaf values

During the March 23, 2022 GEMS RTF Meeting, the RTF members agreed to add text to the GEMS specification describing how GEMS Directives could be used to achieve direct leaf value access (GETs and SETs) without changing the current GEMS 1.4 interface. Mr. Luis Rodriguez offered to write this text and provide example directives.

This "Directive" approach is an alternative to the preferred approach of changing the GEMS standard to generically support direct leaf value access (e.g. via standard "dot notation") - this approach is tracked in GEMS16-1.