Clarify presence rules for scenario ID/name for references

[kleihan]

Orchestra v1.1 added scenarios as top level element and added a numerical identifier. References are now possible by name and/or identifier whereby both are optional but also have a default value.

		<xs:attribute name="scenario" type="fixr:Name_t" default="base">
			<xs:annotation>
				<xs:documentation>The use case of an element, distinguished by workflow, asset class, etc.</xs:documentation>
			</xs:annotation>
		</xs:attribute>
		<xs:attribute name="scenarioId" type="fixr:id_t" default="1">
			<xs:annotation>
				<xs:documentation>Unique identifier of a scenario. Default is '1' for base scenario.</xs:documentation>
			</xs:annotation>
		</xs:attribute>

Does this mean that absence of scenario/scenarioID in a reference makes it "base"/"1"? That would require both name and ID to be present unless it is really the base scenario.

Chapter 3.5 Scenarios should be extended to clarify the referencing of scenarios.