**   au:  An array of integers that define thick-line risers for branches.
    **        The integers are in pairs.  For each pair, the first integer is
    **        is the rail on which the riser should run and the second integer
    **        is the id of the node upto which the riser should run. If there
    **        are no risers, this array does not exist.
    **   mi:  "merge-in".  An array of integer rail positions from which
    **        merge arrows should be drawn into this node.  If the value is
    **        negative, then the rail position is the absolute value of mi[]
    **        and a thin merge-arrow descender is drawn to the bottom of
    **        the screen. This array is omitted if there are no inbound
    **        merges.
    **   ci:  "cherrypick-in". Like "mi" except for cherrypick merges.
    **        omitted if there are no cherrypick merges.
    **    h:  The artifact hash of the object being graphed
    *    br:  The branch to which the artifact belongs
    */
    aiMap = pGraph->aiRailMap;
    for(pRow=pGraph->pFirst; pRow; pRow=pRow->pNext){

      if( colorGraph && pRow->zBgClr[0]=='#' ){
        cgi_printf("\"fg\":\"%s\",", bg_to_fg(pRow->zBgClr));
      }
      /* mi */
      for(i=k=0; i<GR_MAX_RAIL; i++){
        if( pRow->mergeIn[i]==1 ){
          int mi = aiMap[i];
          if( (pRow->mergeDown >> i) & 1 ) mi = -mi;
          if( k==0 ){
            cgi_printf("\"mi\":");
            cSep = '[';
          }
          k++;
          cgi_printf("%c%d", cSep, mi);
          cSep = ',';