Header fields
Content-length: <bytes>
This field indicates length of the body in bytes.
Content-type: <mime type>
This field identifies the content of the body.
The last-modified allows a client to know how recent
his information is. This is helpful for subscription requests and
conditional gets.
Since: <Time>
This field is used by a subscription request to indicate
from what point in time to begin sending INFORM messages. This is
helpful when the client was disconnected from a previous subscription and
wished to resynchronize.
This field is used to specify a range of time.
XWeb URL is the location the client wises all changes
to be forwarded to.
This field is used to convey a transaction identifier.
Update-style: <difference style>
A <difference style> will either be:
full – all information updated, same as a get
difference – encodes just the difference between one state and the
current state
history – encodes the history of changes, including when it was changed,
by whom.
Note that update-style is only a request. The server may return any
form it wishes.
Update-frequency: <freq>
This is a request for a given update period. Note
that this is only a request, the server may send updates as frequently
or infrequently as it wishes.