docs: function checkInvalidHeaderChar(val) {
    val += '';
    if (val.length < 1)
      return false;
    var c = val.charCodeAt(0);
    if ((c <= 31 && c !== 9) || c > 255 || c === 127)
      return true;
    if (val.length < 2)
      return false;
    c = val.charCodeAt(1);
    if ((c <= 31 && c !== 9) || c > 255 || c === 127)
      return true;
    if (val.length < 3)
      return false;
    c = val.charCodeAt(2);
    if ((c <= 31 && c !== 9) || c > 255 || c === 127)
      return true;
    for (var i = 3; i < val.length; ++i) {
      c = val.charCodeAt(i);
      if ((c <= 31 && c !== 9) || c > 255 || c === 127)
        return true;
    }
    return false;
  }