Revised/reordered text.
The definition of XMPP stanzas in &xmppcore; and &xmppim; allows a &MESSAGE; stanza to include any number of child elements that define extended content. The fact that a message stanza may contain multiple instances of extended content can make it difficult for sending entities to know what is appropriate for inclusion in a message stanza and for receiving entities to know exactly how to process a message stanza.
-Consider the following hypothetical example, which as we shall see is invalid.
+Consider the following hypothetical example:
What to make of a message like this? The import seems to be that Romeo, being in a flirtatious mood (&xep0107;) and currently located near Juliet's abode (&xep0080;), would urgently (&xep0131;) like to meet with Juliet (message body) and proposes two convenient places (&xep0020;) for an evening tryst, but no later than midnight (&xep0079;), and for good measure would like to transport the 85th packet of a file transfer. But how is Juliet's client supposed to figure that out? That is, what should her client present to the user? And should Romeo's client even send a monstrosity such as this?
+To clarify such matters, this document introduces the concept of "message stanza profiles". Each profile defines a set of elements that are allowed for use, and each message stanza must only be processed under the rules of a single profile. Therefore, at best, Juliet's client in the above example would process the message for just one of its many intended purposes. At worst, the message would be rejected by Juliet's client as invalid. Romeo's client should not be sending such a monstrosity.
+Elements used in a message stanza are either profile elements (for example, <body> or <data xmlns='http://jabber.org/protocol/ibb'>) or metadata elements (for example, <error> or <amp xmlns='http://jabber.org/protocol/amp'>). A message stanza SHOULD only contain profile elements that are part of the same profile. A message stanza MAY contain as many metadata elements as desired.
+A sender MAY mix elements of different profiles only for the purposes of fallback. For example, it may be useful to include a <body> element in a message that is not intended to be displayed as a text message, in case the recipient does not support the primary profile of the message.
+A receiver MUST only process the message for a single profile. The above example message would be processed either as an IBB data packet or as an instant message, but never both.
+We stipulate the following rules:
+If a message stanza is received that combines multiple profiles, or the profile cannot be determined, the receiving client MAY return a stanza error, which SHOULD be ¬acceptable;.
+What to make of a message like this? The import seems to be that Romeo, being in a flirtatious mood (&xep0107;) and currently located near Juliet's abode (&xep0080;), would urgently (&xep0131;) like to meet with Juliet (message body) and proposes two convenient places (&xep0020;) for an evening tryst, but no later than midnight (&xep0079;). But how is Juliet's client supposed to figure that out? That is, what should her client present to the user? And should Romeo's client even send a monstrosity such as this? (No.)
-To clarify such matters, in this document we introduce the concept of "message stanza profiles".
We propose the following profiles.
+Profiles should be defined in whichever specifications define elements or processing behavior of message stanzas. However, a few profiles are defined here.
The instant messaging (IM) profile is the "default" profile for message stanzas. For example, if a message stanza includes only elements that are defined for the 'jabber:client' namespace then it is in the IM profile. If a message stanza includes both IM profile elements and other elements, the IM elements should be considered a fallback and the profile should be determined based on the other elements if supported (e.g., a data form). A sending entity should limit the elements it includes to IM profile elements, unless the IM elements are a fallback.
The extended content defined in the following specifications is considered to be in the IM profile:
@@ -124,6 +172,7 @@Metadata elements are included to define how the message stanza shall be routed, delivered, or processed in transit. Metadata elements shall not be used to determine which profile applies. If a message stanza includes only metadata elements, it can be considered to have no profile.
+Metadata elements should be defined in whichever specifications define elements or processing behavior of message stanzas. However, a few metadata elements are defined here.
The extended content elements defined in the following specifications are considered to be metadata elements:
We stipulate the following rules:
-Therefore, the example provided in the introduction should never be generated by a sending client because the message combines multiple profiles. If it receives a message stanza that combines multiple profiles, the receiving client MAY return a stanza error, which SHOULD be ¬acceptable;.
-Since each message is unambiguously determined to be of a specific profile, implementations that use filtering to pass message stanzas to an appropriate handler (a very common XMPP implementation approach) need not be concerned with the filtering order. This is because only one handler should ever match on the filter expression.
This document adds no security concerns or consideration above and beyond those specified in the specifications to which it refers.