gml:CodeOrNullListType

List of values on a uniform nominal scale.  List of text tokens.   
      In a list context a token should not include any spaces, so xsd:Name is used instead of xsd:string.  
      A member of the list may be a typed null.  
      If a codeSpace attribute is present, then its value is a reference to 
      a Reference System for the value, a dictionary or code list.