def METHOD_NAME(self, _name, _value, **_params):
    """Extended header setting.
    _name is the header field to add.  keyword arguments can be used to set
    additional parameters for the header field, with underscores converted
    to dashes.  Normally the parameter will be added as key="value" unless
    value is None, in which case only the key will be added.
    Example:
    h.add_header('content-disposition', 'attachment', filename='bud.gif')
    Note that unlike the corresponding 'email.message' method, this does
    *not* handle '(charset, language, value)' tuples: all values must be
    strings or None.
    """
    parts = []
    if _value is not None:
        _value = self._convert_string_type(_value)
        parts.append(_value)
    for k, v in _params.items():
        k = self._convert_string_type(k)
        if v is None:
            parts.append(k.replace('_', '-'))
        else:
            v = self._convert_string_type(v)
            parts.append(_formatparam(k.replace('_', '-'), v))
    self._headers.append((self._convert_string_type(_name), "; ".join(parts)))