Specifies whether the expect "100-request" header
is enabled when a message is sent. Select this check box to enable the expect
"100-request" header. This option is only available if you selected
HTTP 1.1 in the Protocol version field. This option is disabled if
you selected the HTTP 1.0 protocol.
The purpose of the 100 status is to allow a client that is sending a request
message with a request body to determine if the origin server accepts the
request (based on the request headers) before the client sends the request
body. In some cases, you might not want the client to send the body if the
server rejects the message without looking at the body.
The Expect request-header field is used to indicate that particular server
behaviors are required by the client. A server that cannot comply with any
of the expectation values in the Expect field of a request responds with an
appropriate error status.