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;
  }