'Add a new header tuple to the list.
Keyword arguments can specify additional parameters for the header
value, with underscores converted to dashes::
>>> d = Headers()
>>> d.add(\'Content-Type\', \'text/plain\')
>>> d.add(\'Content-Disposition\', \'attachment\', filename=\'foo.png\')
The keyword argument dumping uses :func:`dump_options_header`
behind the scenes.
.. versionadded:: 0.4.1
keyword arguments were added for :mod:`wsgiref` compatibility.'

def add(self, _key, _value, **kw):

    if kw:
        _value = _options_header_vkw(_value, kw)
    _value = _unicodify_header_value(_value)
    self._validate_value(_value)
    self._list.append((_key, _value))
