'The Pragma general-header field is used to include
implementation-specific directives that might apply to any recipient
along the request/response chain.  All pragma directives specify
optional behavior from the viewpoint of the protocol; however, some
systems MAY require that behavior be consistent with the directives.'

@cached_property
def pragma(self):

    return parse_set_header(self.environ.get('HTTP_PRAGMA', ''))
