public ObjectMember(StringToken objectName, Colon colon, MemberValue objectValue) 
     : base(objectName, colon, objectValue)
 {
     this.objectName = objectName;
     this.colon = colon;
     this.objectValue = objectValue;
 }
 protected virtual Colon VisitColon(Colon node)
 {
     return VisitSyntaxNode(node) as Colon;
 }
 protected override Colon VisitColon(Colon node)
 {
     visitedColon = true;
     Assert.IsTrue(node.Value == ":");
     return base.VisitColon(node);
 }