code: protected void open() {
  
          if (!m_enabled) {
              return;
          }
          m_openClose.setDown(true);
          if (m_maxCellWidth == 0) {
              initMaxCellWidth();
          }
          int selectorWidth = m_maxCellWidth;
          // should not be any wider than the actual window
          int windowWidth = Window.getClientWidth();
          if (m_maxCellWidth > windowWidth) {
              selectorWidth = windowWidth - 10;
          }
          // if the resize option is deactivated the popup should not be wider than the selectbox.
          // Default its true.
          if (!m_resizePopup) {
              selectorWidth = m_opener.getOffsetWidth() - 2;
          }
          m_popup.setWidth(selectorWidth + "px");
          m_popup.setWidget(m_selector);
          m_popup.show();
  
          positionPopup();
      }
docs: Internal method which is called when the selector is opened.<p>