Inheritance: IToken
        internal void InsertAt( int insertionPoint, string token )
        {
            var ts = new Token( token );

            if( insertionPoint == _token.Count ) _token.Add( ts );
            else _token.Insert( insertionPoint, ts );

            if( CollectionChanged != null )
                CollectionChanged( this, new NotifyCollectionChangedEventArgs( NotifyCollectionChangedAction.Add, ts ) );
        }