docs: function _fnVisbleColumns( oS )
  		{
  			var iVis = 0;
  			for ( var i=0 ; i<oS.aoColumns.length ; i++ )
  			{
  				if ( oS.aoColumns[i].bVisible === true )
  				{
  					iVis++;
  				}
  			}
  			return iVis;
  		}