'Adds a new value for the given key.'

def add(self, name, value):

    norm_name = _normalized_headers[name]
    self._last_key = norm_name
    if (norm_name in self):
        dict.__setitem__(self, norm_name, ((native_str(self[norm_name]) + ',') + native_str(value)))
        self._as_list[norm_name].append(value)
    else:
        self[norm_name] = value
