code: function mergeListSiblings( listNode )
  	{
  		var mergeSibling;
  		( mergeSibling = function( rtl )
  		{
  			var sibling = listNode[ rtl ? 'getPrevious' : 'getNext' ]( nonEmpty );
  			if ( sibling &&
  			     sibling.type == CKEDITOR.NODE_ELEMENT &&
  			     sibling.is( listNode.getName() ) )
  			{
  				// Move children order by merge direction.(#3820)
  				mergeChildren( listNode, sibling, null, !rtl );
  
  				listNode.remove();
  				listNode = sibling;
  			}
  		} )();
  		mergeSibling( 1 );
  	}
docs: Merge list adjacent, of same type lists.