int da = _domNthCache_A.distance(parent, n);
int db = _domNthCache_B.distance(parent, n);
// the "better" cache should never walk more than 1/2 len
Dom x = null;
boolean bInvalidate = (db - _domNthCache_B._len / 2 > 0) &&
(db - _domNthCache_B._len / 2 - domNthCache.BLITZ_BOUNDARY > 0);
boolean aInvalidate = (da - _domNthCache_A._len / 2 > 0) &&
(da - _domNthCache_A._len / 2 - domNthCache.BLITZ_BOUNDARY > 0);
if (da <= db)