XTCE12 — Enum Alarm List should be optional

The enum alarm list is required in the syntax. But other alarms types are available for enums, and it is possible that one may require one of them but not have need to define an explicit enum alarm list. The syntax prevents this from occurring. Perhaps the enum list element should be optional.

Allow for no EnumerationAlarmList element in EnumeratedDataType

Propose to resolve to allow for EnumerationAlarmList to be optional in the EnumeratedDataType definition. This does have the side effect of allowing DefaultAlarm to have empty content, which is perhaps not so bad.

Add the @minOccurs = 0 attribute to the definition of the EnumerationAlarmList element in the complex type below. The parent elements are shown for the contextual location of the change.

<complexType name="EnumerationAlarmType">
<annotation>
<documentation>Describe alarm conditions specific to the enumeration data type, extends the basic AlarmType with an EnumerationAlarmList. See EnumeratedParameterType.</documentation>
</annotation>
<complexContent>
<extension base="xtce:AlarmType">
<sequence>
<element name="EnumerationAlarmList" type="xtce:EnumerationAlarmListType" minOccurs="0"/>