code: protected void continueDragging(MouseMoveEvent event) {
  
          if (m_dragging) {
              int absX = event.getX() + getAbsoluteLeft();
              int absY = event.getY() + getAbsoluteTop();
  
              // if the mouse is off the screen to the left, right, or top, don't
              // move the dialog box. This would let users lose dialog boxes, which
              // would be bad for modal popups.
              if ((absX < m_clientLeft) || (absX >= m_windowWidth) || (absY < m_clientTop)) {
                  return;
              }
  
              setPopupPosition(absX - m_dragStartX, absY - m_dragStartY);
          }
      }
docs: Called on mouse move in the caption area, continues dragging if it was
  started by {@link #beginDragging}.
  
  @see #beginDragging
  @see #endDragging
  @param event the mouse move event that continues dragging