pRow->iRail = ++p->mxRail;
      pRow->railInUse = 1<<pRow->iRail;
      continue;
    }
    if( pDesc->aiRaiser[pDesc->iRail]==0 && pDesc->zBranch==pRow->zBranch ){
      pRow->iRail = pDesc->iRail;
    }else{
      pRow->iRail = findFreeRail(p, 0, pDesc->idx, inUse, 0);
      pRow->iRail = findFreeRail(p, 0, pDesc->idx, inUse, pDesc->iRail);
    }
    pDesc->aiRaiser[pRow->iRail] = pRow->idx;
    mask = 1<<pRow->iRail;
    if( pRow->isLeaf ){
      inUse &= ~mask;
    }else{
      inUse |= mask;