docs: function between (a, b) {
  
      var s = '', i = 0
  
      while (true) {
  
        var _a = chars.indexOf(a[i])
        var _b = chars.indexOf(b[i])
       
        if(_a == -1) _a = 0
        if(_b == -1) _b = chars.length - 1
  
        i++
  
        var c = chars[
            _a + 1 < _b 
          ? Math.round((_a+_b)/2)
          : _a
        ]
  
        s += c
  
        if(a < s && s < b && c != exports.lo)
          return s;
      }
    }