anchor.diff:  
   xMLRealValue: xMLNumericRealValue | xMLSpecialRealValue ;
   
  -xMLNumericRealValue: '-'? realnumber ;
  +xMLNumericRealValue: '-'? REALNUMBER ;
   
   xMLSpecialRealValue: emptyElementReal | textReal ;
   
  
positive.code: 
  parameterizedType: simpleDefinedType actualParameterList ;
  
  simpleDefinedType: externalTypeReference | typereference ;
  
  parameterizedValue: simpleDefinedValue actualParameterList ;
  
  simpleDefinedValue: externalValueReference | valuereference ;
  
  parameterizedValueSetType: simpleDefinedType actualParameterList ;
  
  
negative.code: setting: type | value | valueSet | object | objectSet ;
  
  // Chapter 12 Information object set definition and assignment
  objectSetAssignment: OBJECTSETREFERENCE definedObjectClass '::=' objectSet ;
  
  objectSet: '{' objectSetSpec '}' ;
  
  