A grammar extension to the Scenarios module has special considerations. It specifies an XML file containing an expression grammar definition just like those described above, with information specific to this module, including:
Grammar elements that correspond to custom scenario actions, events and conditions
Additional information governing the generation of XML fragments that provide the PDL (Process Description Language) corresponding to grammar elements
Special-purpose tags for scenario-related grammatical expressions and attributes
Note that the chapter Adding Custom Events, Actions, and Conditions to Scenarios contains a detailed example of extending the grammar editor for scenarios. It shows how to add a custom condition to the grammar editor. The example is in the section Extending the Expression Editor.