docs: function _fnColumnIndexToVisible( oSettings, iMatch )
  		{
  			var iVisible = -1;
  			for ( var i=0 ; i<oSettings.aoColumns.length ; i++ )
  			{
  				if ( oSettings.aoColumns[i].bVisible === true )
  				{
  					iVisible++;
  				}
  				
  				if ( i == iMatch )
  				{
  					return oSettings.aoColumns[i].bVisible === true ? iVisible : null;
  				}
  			}
  			
  			return null;
  		}