code: @SuppressWarnings("unchecked")
      T getItemAt(int position) {
          if (position > getLength())
              throw new IllegalArgumentException("Index " + position
                  + " is greater than " + getLength()
                  + " - the length of this edge.");
          return (T) sequence.getItem(start + position);
      }
docs: Retrieves the item at given position within the current edge.
  
  @param position The index of the item to retrieve relative to the start of
  edge.
  @return The item at position.
  @throws IllegalArgumentException when the position exceeds the length of the current edge.