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@ -10,7 +10,7 @@
<abstract>In order to keep all IM clients for a user engaged in a conversation, outbound messages are carbon-copied to all interested resources.</abstract>
&LEGALNOTICE;
<number>0280</number>
<status>Deferred</status>
<status>Experimental</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
@ -19,6 +19,7 @@
<spec>XEP-0001</spec>
<spec>XEP-0030</spec>
<spec>XEP-0085</spec>
<spec>XEP-0296</spec>
</dependencies>
<supersedes>
<spec>XEP-0259</spec>
@ -31,6 +32,18 @@
<email>jhildebr@cisco.com</email>
<jid>jhildebr@cisco.com</jid>
</author>
<author>
<firstname>Matthew</firstname>
<surname>Miller</surname>
<email>linuxwolf@outer-planes.net</email>
<jid>linuxwolf@outer-planes.net</jid>
</author>
<revision>
<version>0.2</version>
<date>2011-07-10</date>
<initials>mm</initials>
<remark><p>Changed enabling and disabling to use separate elements rather than attributes; ensured all elements in the examples have their namespaces more explicitly defined; used message forwarding for carbon copies.</p></remark>
</revision>
<revision>
<version>0.1</version>
<date>2010-05-03</date>
@ -51,23 +64,10 @@
</revision>
</header>
<section1 topic='Introduction' anchor='intro'>
<p>At the time of original writing of this XEP, many XMPP servers
handle message stanzas sent to a user@host (or "bare") JID with no
resource by delivering that message only to the resource with the
highest priority for the target user. Some server implementations,
however, have chosen to send these messages to all of the online
resources for the target user. If the target user is online with
multiple resources when the original message is sent, a conversation
ensues on one of the user's devices; if the user subsequently
switches devices, parts of the conversation may end up on the
alternate device, causing the user to be confused, misled, or
annoyed.</p>
<p>At the time of original writing of this XEP, many XMPP servers handle message stanzas sent to a user@host (or "bare") JID with no resource by delivering that message only to the resource with the highest priority for the target user. Some server implementations, however, have chosen to send these messages to all of the online resources for the target user. If the target user is online with multiple resources when the original message is sent, a conversation ensues on one of the user's devices; if the user subsequently
switches devices, parts of the conversation may end up on the alternate device, causing the user to be confused, misled, or annoyed.</p>
<p>This XEP defines an approach for ensuring that all of my devices
get both sides of all conversations in order to avoid user
confusion. As a pleasant side-effect, information about the current
state of a conversation is shared between all of a user's clients
that implement this protocol.</p>
<p>This XEP defines an approach for ensuring that all of my devices get both sides of all conversations in order to avoid user confusion. As a pleasant side-effect, information about the current state of a conversation is shared between all of a user's clients that implement this protocol.</p>
</section1>
<section1 topic='Requirements' anchor='reqs'>
@ -89,74 +89,65 @@
</section1>
<section1 topic='Use Cases' anchor='usecases'>
<section2 topic='Discovering Support' anchor='disco'>
<p>If a server implements the Message Carbons capability, it MUST specify the
'urn:xmpp:carbons:0' feature in its service discovery
information features as specified in &xep0030; or section 6.3 of &xep0115;.
Clients MUST NOT enable or disable Carbons if their server does
not support this feature.</p>
<p>If a server implements the Message Carbons capability, it MUST specify the "urn:xmpp:carbons:1" feature in its service discovery information features as specified in &xep0030; or section 6.3 of &xep0115;. Clients SHOULD NOT attempt to enable or disable Carbons if their server does not support this feature.</p>
<example caption='Client requests information about its own server'><![CDATA[
<iq type='get'
<iq xmlns='jabber:client'
type='get'
from='romeo@montague.net/orchard'
id='info1'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>]]></example>
<example caption='Server responds with Carbons feature'><![CDATA[
<iq type='get'
<iq xmlns='jabber:client'
type='get'
to='romeo@montague.net/home'
from='montague.net'
id='info1'>
<query xmlns='http://jabber.org/protocol/disco#info'>
...
<feature var='urn:xmpp:carbons:0'/>
<feature var='urn:xmpp:carbons:1'/>
...
</query>
</iq>]]></example>
</section2>
<section2 topic='Enabling Carbons' anchor='enabling'>
<p>Servers MUST NOT enable the Carbons protocol for a client by
default, since unmodified clients might be confused by the new
protocol. When a client wants to participate in the Carbons
protocol, it sends an IQ set to enable the protocol.</p>
<p>Servers MUST NOT enable the Carbons protocol for a client by default, since unmodified clients might be confused by the new protocol. When a client wants to participate in the Carbons protocol, it sends an IQ set to enable the protocol.</p>
<example caption='Client enables Carbons'><![CDATA[
<iq type='set' id='enable1'>
<carbons var='urn:xmpp:carbons:0' mode='enable'/>
<iq xmlns='jabber:client'
type='set'
id='enable1'>
<enable var='urn:xmpp:carbons:1'/>
</iq>]]></example>
<p>Carbons will generally be enabled before the client sends the
first undirected presence, to ensure that all inbound messages
will be delivered according to the Carbon rules. The server will
respond with an IQ result when Carbons are enabled:</p>
<p>Carbons will generally be enabled before the client sends the first undirected presence, to ensure that all inbound messages will be delivered according to the Carbon rules. The server will respond with an IQ result when Carbons are enabled:</p>
<example caption='Server acknowledges Carbons enablement'><![CDATA[
<iq type='result' id='enable1'/>]]></example>
<iq xmlns='jabber:client'
type='result'
id='enable1'/>]]></example>
</section2>
<section2 topic='Disabling Carbons' anchor='disabling'>
<p>Some clients might want to disable Carbons. An example of this
might be a mobile client that wants Carbons when the application
is in the foreground, and disabled when it is in the background.
To disable Carbons, clients send an IQ set:</p>
<p>Some clients might want to disable Carbons. An example of this might be a mobile client that wants Carbons when the application is in the foreground, and disabled when it is in the background. To disable Carbons, clients send an IQ set:</p>
<example caption='Client disables Carbons'><![CDATA[
<iq type='set' id='disable1'>
<carbons var='urn:xmpp:carbons:0' mode='disable'/>
<iq xmlns='jabber:client'
type='set'
id='disable1'>
<disable var='urn:xmpp:carbons:1'/>
</iq>]]></example>
<p>The server will respond with an IQ result when Carbons are disabled:</p>
<example caption='Server acknowledges Carbons enablement'><![CDATA[
<iq type='result' id='disable1'/>]]></example>
<iq xmlns='jabber:client'
type='result'
id='disable1'/>]]></example>
</section2>
<section2 topic='Error Cases' anchor='errors'>
<p>Enabling or disabling Carbons may fail in the several ways. If
one of these errors is returned, the server MUST keep the previous
state, where the initial state is Carbons disabled. For example,
if the first enable returns an error, the server MUST NOT enable
Carbons.</p>
<p>Enabling or disabling Carbons may fail in the several ways. If one of these errors is returned, the server MUST keep the previous state, where the initial state is Carbons disabled. For example, if the first enable returns an error, the server MUST NOT enable Carbons.</p>
<section3 topic='bad-request' anchor='bad-request'>
<p>The sender has sent a stanza containing XML that does not
conform to the appropriate schema or that cannot be processed.
One example is an IQ stanza that includes an unrecognized value
of the 'type' attribute. Another is changing to the state that
is already in effect (enabling Carbons a second time).</p>
<example caption='Error: bad-request'><![CDATA[<iq id='enable1'
<p>The sender has sent a stanza containing XML that does not conform to the appropriate schema or that cannot be processed. One example is an IQ stanza that includes an unrecognized value of the 'type' attribute. Another is changing to the state that is already in effect (enabling Carbons a second time).</p>
<example caption='Error: bad-request'><![CDATA[
<iq xmlns='jabber:client'
id='enable1'
type='error'>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
@ -168,7 +159,9 @@
that does not support the protocol. This SHOULD NOT happen in
practice, because clients MUST check for server support before
sending their request.</p>
<example caption='Error: feature-not-implemented'><![CDATA[<iq id='enable1'
<example caption='Error: feature-not-implemented'><![CDATA[
<iq xmlns='jabber:client'
id='enable1'
type='error'>
<error type='cancel'>
<feature-not-implemented xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
@ -178,7 +171,9 @@
<section3 topic='forbidden' anchor='forbidden'>
<p>The sender does is forbidden by policy from enabling or
disabling Carbons.</p>
<example caption='Error: forbidden'><![CDATA[<iq id='enable1'
<example caption='Error: forbidden'><![CDATA[
<iq xmlns='jabber:client'
id='enable1'
type='error'>
<error type='auth'>
<forbidden xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
@ -190,7 +185,9 @@
This might occur in a multi-domain deployment, where
administrators of one domain allow Carbons, but another does
not.</p>
<example caption='Error: not-allowed'><![CDATA[<iq id='enable1'
<example caption='Error: not-allowed'><![CDATA[
<iq xmlns='jabber:client'
id='enable1'
type='error'>
<error type='cancel'>
<not-allowed xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
@ -198,18 +195,11 @@
</iq>]]></example>
</section3>
</section2>
<section2 topic='Inbound Messages' anchor='inbound'>
<p>Messages of type chat that are addressed to the bare JID
(localpart@domain) MUST be copied by the receiving server to all of the
resources for that user that have non-negative presence priority
and have not filtered messages through some other means. The
process of making copies is known as "forking." The receiving
server SHOULD NOT modify the 'to' address of the forked
messages.</p>
<section2 topic='Receiving Messages' anchor='inbound'>
<p>Messages of type chat that are addressed to the bare JID (localpart@domain) MUST be copied by the receiving server to all of the resources for that user that have non-negative presence priority and have not filtered messages through some other means. The process of making copies is known as "forking."</p>
<example caption='Juliet sends Romeo an undirected message, which is forked'><![CDATA[
<message
<message xmlns='jabber:client'
from='juliet@example.com/balcony'
to='romeo@example.net'
type='chat'>
@ -220,49 +210,43 @@
... each of romeo@example.net's resources receives this stanza verbatim
]]></example>
<p>Messages of type "chat" that are addressed to a full JID
(localpart@domain/resource) MUST be sent by the receiving server to the
addressed resource, and MUST also be sent to all of the
Carbons-enabled resources for the receiving user. The goal of
the copies to Carbons-enabled resources is to allow those clients
to have both halves of *all* IM conversations, including messages
that are sent from clients that lock in to particular resources.</p>
<p>Messages of type "chat" that are addressed to a full JID (localpart@domain/resource) MUST be sent by the receiving server to the addressed resource, and MUST also be sent to all of the Carbons-enabled resources for the receiving user. The goal of the copies to Carbons-enabled resources is to allow those clients to have both halves of <strong>*all*</strong> IM conversations, including messages that are sent from clients that lock in to particular resources.</p>
<p>The copies sent to the Carbon-enabled resources are wrapped using &xep0297;. The wrapping message SHOULD maintain the same 'type', 'from', and 'id' attribute values (if any), while the 'to' attribute SHOULD be the full JID of the resource receiving the copy. The content of the wrapping message MUST contain a &lt;forwarded xmlns='urn:xmpp:forward:0'/&gt; which contains the original message (properly namespaced as "jabber:client") and a &lt;received xmlns='urn:xmpp:carbons:1'/&gt; element:</p>
<example caption='Juliet sends Romeo a directed message'><![CDATA[
<message xmlns='jabber:client'
from='juliet@example.com/balcony'
to='romeo@example.net/garden'
type='chat'>
<body>What man art thou that, thus bescreen'd in night, so stumblest on my counsel?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
</message>
]]></example>
<example caption='Server sends carbon to Romeo&apos;s other clients'><![CDATA[
<message xmlns='jabber:client'
from='juliet@example.com/balcony'
to='romeo@example.net/home'
type='chat'>
<forwarded xmlns='urn:xmpp:forward:0'>
<received xmlns='urn:xmpp:carbons:1'/>
<message xmlns='jabber:client'
from='juliet@example.com/balcony'
to='romeo@example.net/garden'
type='chat'>
<body>What man art thou that, thus bescreen'd in night, so stumblest on my counsel?</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
</message>
</forwarded>
</message>
]]></example>
</section2>
<section2 topic='Sending Messages' anchor='outbound'>
<p>Carbons clients want to have copies of messages going in <em>both</em> directions for other resources associated with the same user. To that end, messages of type "chat" that are sent from any resource MUST be copied by the sending server to each of the resources that have enabled Carbons, but are not the sending resource.</p>
<section2 topic='Sending Messages' anchor='sending'>
<p>Once most of the clients that are deployed have implemented
Carbons, clients MAY choose to always send chat type messages to
the bare JID. Until then, traditional resource locking is
RECOMMENDED. (Note: another XEP might be written to document
traditional resource locking, if the documentation in &xmppim;
is not sufficient.)</p>
<p>The copies sent to the Carbon-enabled resources are wrapped using Message Forwarding. The wrapping message SHOULD maintain the same 'type', 'from', and 'id' attribute values, while the 'to' attribute SHOULD be the full JID of the resource receiving the copy. The content of the wrapping message MUST contain a &lt;forwarded xmlns='urn:xmpp:forward:0'/&gt; which contains the original message (properly namespaced as "jabber:client") and a &lt;sent xmlns='urn:xmpp:carbons:1'/> element:</p>
<p>Also note that &xep0085; recommends sending chat state
notifications as chat type messages, which means that they will be
subject to Carbon-copying. This is intentional.</p>
</section2>
<section2 topic='Outbound Message Carbon Copies' anchor='outbound'>
<p>Carbons clients want to have copies of messages going in
<em>both</em> directions for other resources associated with the
same user. To that end, messages of type chat that are sent from
any resource MUST be copied by the sending server to each of the
resources that have enabled Carbons, but are not the sending
resource. Note that the 'to' address will be the original target of
the message (bare JID, as above), and the 'from' address will
contain the full JID (localpart@domain/resource) of the sending
resource. The 'to' address not matching the JID of the session is
somewhat unprecedented in XMPP, which is why Carbons must be
explicitly enabled.</p>
<p>Messages that have carbon copies sent back to Carbons-enabled
resources MUST NOT be copied back to the originating client. The
copies MUST have the full JID (localpart@domain/resource) of the sender
as the 'from' address. The copies MUST include a sent element in
the urn:xmpp:carbons:0 namespace.</p>
<example caption='Romeo responds to Juliet, which is Carboned'><![CDATA[
<message
<example caption='Romeo responds to Juliet'><![CDATA[
<message xmlns='jabber:client'
to='juliet@example.com/balcony'
from='romeo@example.net/home'
type='chat'>
@ -270,46 +254,43 @@
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
</message>]]></example>
<example caption='Romeo&apos;s OTHER Carbons-enabled clients
<example caption='Romeo&apos;s other Carbons-enabled clients
receive a copy'><![CDATA[
<message
<message xmlns='jabber:client'
from='romeo@example.net/home'
to='romeo@example.net/garden'
type='chat'>
<forwarded xmlns='urn:xmpp:forward:0'>
<sent xmlns='urn:xmpp:carbons:1'/>
<message xmlns='jabber:client'
to='juliet@example.com/balcony'
from='romeo@example.net/home'
type='chat'>
<body>Neither, fair saint, if either thee dislike.</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<sent xmlns='urn:xmpp:carbons:0'/>
</message>
</message>]]></example>
</section2>
<section2 topic='Avoiding Carbons for a single message' anchor='avoiding'>
<p>Some clients might want to avoid carbons on a single message,
while still keeping all of the other semantics of Carbon support.
This might be useful for clients sending end-to-end encrypted
messages, for example.</p>
<p>Some clients might want to avoid carbons on a single message, while still keeping all of the other semantics of Carbon support. This might be useful for clients sending end-to-end encrypted messages, for example.</p>
<p>To avoid a message being Carbon-copied to its other resources,
the sending client MUST add a private element in the
urn:xmpp:carbons:0 namespace. When the sending server receives
the message, it MUST NOT make carbon copies to the other
Carbons-enabled resources, and MUST remove the private element
before forwarding the message to the intended recipient.</p>
<p>To avoid a message being Carbon-copied to its other resources, the sending client MUST add a private element in the "urn:xmpp:carbons:1" namespace. When the sending server receives the message, it MUST NOT make carbon copies to the other Carbons-enabled resources, and MUST remove the private element before forwarding the message to the intended recipient.</p>
<p>Note: use of the private mechanism will lead to partial
conversations on other devices. This is the intended effect.</p>
<p><strong>Note:</strong> use of the private mechanism will lead to partial conversations on other devices. This is the intended effect.</p>
<example caption='Romeo sends to Juliet, avoiding Carbon copies'><![CDATA[
<message
<message xmlns='jabber:client'
to='juliet@example.com'
from='romeo@example.net/home'
type='chat'>
<body>Neither, fair saint, if either thee dislike.</body>
<thread>0e3141cd80894871a68e6fe6b1ec56fa</thread>
<private xmlns='urn:xmpp:carbons:0'/>
<private xmlns='urn:xmpp:carbons:1'/>
</message>]]></example>
<example caption='Romeo&apos;s server removes the private tag before forwarding, and does NOT send carbon copies to Romeo&apos;s other resources'><![CDATA[
<message
<message xmlns='jabber:client'
to='juliet@example.com'
from='romeo@example.net/home'
type='chat'>
@ -320,56 +301,29 @@
</section1>
<section1 topic='Business Rules' anchor='rules'>
<section2 topic='Interaction with Chat States' anchor='chatstates'>
<p>Clients that implement Carbons MAY take special use of
&xep0085; notifications.</p>
<p>It is RECOMMENDED that upon receiving an outbound <em>gone</em>
chat state (as a carbon copy) for a given conversation, that
conversation be removed from user display as if the user on the
copied client had terminated the conversation. In order to
prevent unwanted termination of conversations on other resources,
clients SHOULD NOT send <em>gone</em> chat states on logout, but
instead SHOULD count on the unavailable presence to convey the change
in attention.</p>
<p>Upon receiving an outbound notification of any chat state other
than <em>gone</em>, the copied client MAY conclude that the
sending client has taken responsibility for the conversation, and
make appropriate user interface modifications. For example,
notifications could be muted on non-primary devices.</p>
<p>Note that &xep0085; recommends sending chat state
notifications as chat type messages, which means that they will be
subject to Carbon-copying. This is intentional.</p>
<p>Additionally, clients that implement Carbons MAY take special use of chat state notifications:</p>
<ul>
<li>Upon receiving an inbound or outbound <em>gone</em> chat state (as a carbon copy) for a given conversation, that conversation SHOULD be removed from user display as if the user on the copied client had terminated the conversation. In order to prevent unwanted termination of conversations on other resources, clients SHOULD NOT send <em>gone</em> chat states on logout, but instead SHOULD count on the unavailable presence to convey the change in attention.</li>
<li>Upon receiving an outbound notification of any chat state other than <em>gone</em>, the copied client MAY conclude that the sending client has taken responsibility for the conversation, and make appropriate user interface modifications. For example, notifications could be suppressed on devices receiving the Carbon-copies.</li>
</ul>
</section2>
<section2 topic='Handling of errors' anchor='errors'>
<p>When a receiving server attempts to deliver a forked message,
and that message bounces with an error for any reason, the
receiving server MUST NOT forward that error back to the original
sender. The receiving server SHOULD use the sent element in the
bounce to determine that an error is from a forked message.</p>
<p>This rule is used to prevent some of the half-failure modes
that have been an issue in other prototocols.</p>
<p>When a receiving server attempts to deliver a forked message, and that message bounces with an error for any reason, the receiving server MUST NOT forward that error back to the original sender. The receiving server SHOULD use the sent element in the bounce to determine that an error is from a forked message.</p>
<p>This rule is used to prevent some of the half-failure modes that have been an issue in other prototocols.</p>
</section2>
<section2 topic='Auto-responses' anchor='auto-responses'>
<p>Clients that automatically respond to messages for any reason
(e.g. when in DND presence state) MUST take adequate care when
enabling Carbons in order to prevent storms or loops. Carbon
copies of outbound messages MUST NOT be auto-replied to under any
circumstances. Forked inbound messages SHOULD NOT be auto-replied
to, unless the client has some way of knowing that the receiver
will not receive more than one auto-reply from other similar
clients for the same user.</p>
<p>Clients that automatically respond to messages for any reason (e.g. when in the "dnd" presence show state) MUST take adequate care when enabling Carbons in order to prevent storms or loops. Carbon copies of messages MUST NOT be auto-replied to under any circumstances. Forked inbound messages SHOULD NOT be auto-replied to, unless the client has some way of ensuring no more than one auto-reply is sent from all of its user's resources.</p>
</section2>
<section2 topic='Mobile Considerations' anchor='mobile'>
<p>Since mobile devices often must pay for network traffic based
on usage, the enablement of Carbons for such devices should be
undertaken advisedly. More complicated mechanisms for controlling
the Carbon-copying or forking of individual conversations may need
to be added to deal with mobile clients in the future.</p>
<p>Since mobile devices often must pay for network traffic based on usage, the enablement of Carbons for such devices should be undertaken advisedly. More complicated mechanisms for controlling the Carbon-copying or forking of individual conversations may need to be added to deal with mobile clients in the future.</p>
</section2>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>The security model assumed by this document is that all of the
resources for a single user are in the same trust boundary.</p>
<p>Outbound chat messages that are encrypted end-to-end are not often
useful to receive on other resources. As such, they should use the
private element specified above to avoid such copying, unless the
encryption mechanism is adjusted to have knowledge of Carbons.</p>
<p>The security model assumed by this document is that all of the resources for a single user are in the same trust boundary.</p>
<p>Outbound chat messages that are encrypted end-to-end are not often useful to receive on other resources. As such, they should use the &lt;private/&gt; element specified above to avoid such copying, unless the encryption mechanism is able to accommodate this protocol.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
<p>This document requires no interaction with &IANA;.</p>
@ -378,7 +332,7 @@
<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
<p>This specification defines the following XML namespace:</p>
<ul>
<li>urn:xmpp:carbons:0</li>
<li>urn:xmpp:carbons:1</li>
</ul>
<p>Upon advancement of this specification from a status of Experimental to a status of Draft, the &REGISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
</section2>
@ -392,31 +346,20 @@
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:carbons:0'
xmlns='urn:xmpp:carbons:0'
targetNamespace='urn:xmpp:carbons:1'
xmlns='urn:xmpp:carbons:1'
elementFormDefault='qualified'>
<xs:element name='carbons'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute name='mode' use='required'>
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="enable"/>
<xs:enumeration value="disable"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='disable' type='empty'/>
<xs:element name='sent' type='empty'/>
<xs:element name='enable' type='empty'/>
<xs:element name='private' type='empty'/>
<xs:element name='received' type='empty'/>
<xs:element name='sent' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
@ -427,6 +370,6 @@
]]></code>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
<p>The author wishes to thank Patrick Barry, Teh Chang, Jack Erwin, Craig Kaes, Kathleen McMurry, Matt Miller, Tory Patnoe, Peter Saint-Andre, and Ben Schumacher for their feedback.</p>
<p>The authors wish to thank Patrick Barry, Teh Chang, Jack Erwin, Craig Kaes, Kathleen McMurry, Tory Patnoe, Peter Saint-Andre, and Ben Schumacher for their feedback.</p>
</section1>
</xep>