Name
x — Optional
Synopsis
<message to='dj@yak' type='chat' from='sabine@yak/laptop'>
<body>Hi - let me know when you get back. Thanks.</body>
<x xmlns='jabber:x:delay' from='dj@yak' stamp='20010514T14:44:09'>
Offline Storage
</x>
</message>
The <x/> subelement is special.
While the other subelements like
<body/> and
<thread/> are fixed into the
Jabber building blocks design, the
<x/> subelement allows
<message/> elements to be
extended to suit requirements. What the
<x/> subelement does is
provide an anchor point for further information to be attached to messages in a
structured way.
The information attached to a message is often called the payload. Multiple anchor points can be used to convey multiple payloads, and each one must be qualified using a namespace.
Just as the content of XML streams is qualified by a namespace (one
from the list in Table 5-2
earlier in this chapter), so the content of
the <x/>
attachment must
be qualified. There are a number of Jabber-standard namespaces that are
defined for various purposes. One of these,
jabber:x:delay, is used in the
example. These standard namespaces are described in Chapter 6. But there’s
nothing to stop you defining your own namespace to describe (and qualify)
the data that you wish to transport in a
<message/>. Namespaces beginning
jabber: are reserved; anything else is OK.
Briefly, you can see how payloads are attached from the
example. For every <x/>
subelement, there’s an xmlns attribute that qualifies it, and the ...
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