docs: function showPopup(editor, popup, button) {
  
      var offset, left, top, $popup = $(popup);
  
      // Determine the popup location
      if (button) {
        var $button = $(button);
        offset = $button.offset();
        left = --offset.left;
        top = offset.top + $button.height();
      }
      else {
        var $toolbar = editor.$toolbar;
        offset = $toolbar.offset();
        left = Math.floor(($toolbar.width() - $popup.width()) / 2) + offset.left;
        top = offset.top + $toolbar.height() - 2;
      }
  
      // Position and show the popup
      hidePopups();
      $popup.css({left: left, top: top})
        .show();
  
      // Assign the popup button and click event handler
      if (button) {
        $.data(popup, BUTTON, button);
        $popup.bind(CLICK, {popup: popup}, $.proxy(popupClick, editor));
      }
  
      // Focus the first input element if any
      setTimeout(function() {
        $popup.find(":text,textarea").eq(0).focus().select();
      }, 100);
  
    }