The grammar element for a custom action must have a special id: the prefix action- followed by the action’s name, as specified in scenarioManager.xml. The optional <element-icon> tag may be used to provide an icon (specified as a class loader resource path). For instance, if you were defining an expression for the custom event MyAction, you would define the event in the grammar as follows:

<sequence id="action-MyAction">
  <element-icon>icon-resource-path</element-icon>
  ...
</sequence>