docs: function getPrevKeyWith( keys, fullSid, ndx ) {
  
  		ndx = ndx >= 0 ? ndx : ndx + keys.length;
  
  		for ( ; ndx >= 0; ndx -- ) {
  
  			var key = keys[ ndx ];
  
  			if ( key.hasTarget( fullSid ) ) {
  
  				return key;
  
  			}
  
  		}
  
  		return null;
  
  	}