hdrs‘s “Expect” header according to
SOUP_EXPECTATION_CONTINUE is the only known expectation
value. You should set this value on a request if you are sending a
large message body (eg, via POST or PUT), and want to give the
server a chance to reject the request after seeing just the headers
(eg, because it will require authentication before allowing you to
post, or because you’re POSTing to a URL that doesn’t exist). This
saves you from having to transmit the large request body when the
server is just going to ignore it anyway.
The expectations to set.