gml:AbstractValue is an abstract element which acts as the head of a substitution group which contains gml:AbstractScalarValue, gml:AbstractScalarValueList, gml:CompositeValue and gml:ValueExtent, and (transitively) the elements in their substitution groups.<br/>These elements may be used in an application schema as variables, so that in an XML instance document any member of its substitution group may occur.<br/>