The required val attribute is a Boolean constant given as an enumeration.
Source
<xs:complexType name="ConstantIsType"><xs:annotation><xs:documentation>The ConstantIsType evaluates to true if the val is QIF_TRUE and evaluates to false if the val is QIF_FALSE.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="BooleanExpressionBaseType"><xs:attribute name="val" type="BooleanConstantEnumType" use="required"><xs:annotation><xs:documentation>The required val attribute is a Boolean constant given as an enumeration.</xs:documentation></xs:annotation></xs:attribute></xs:extension></xs:complexContent></xs:complexType>
<xs:attribute name="val" type="BooleanConstantEnumType" use="required"><xs:annotation><xs:documentation>The required val attribute is a Boolean constant given as an enumeration.</xs:documentation></xs:annotation></xs:attribute>