code: function incChar(char, base = 10) {
    let val = charToVal(char);
    if (val < 0) throw new Error('in incChar, invalid character');
    val = (val + 1) % base;
    return consts.alphabet[val];
  }
docs: /* Increment a character to the succeeding character in consts.alphabet, modulo the given base.
  *