Customizing the metamodel : Keywords for USRPROPS : REQUIRED
  
REQUIRED
Specifies that a property must be filled in by the user to enable the diagram or definition to be created. The property will automatically appear in the initial Name dialog for the diagram or definition.
Example
This example requires that the user fills in a value for the XML Schema property to create the XML Element Entity definition.
DEFINITION "XML Element Entity" { PROPERTY "XML Schema" { Key Edit ONEOF "XML Schema" Relate By "is keyed by" Required Readonly } }