path: root/doc/rfc/rfc5023.txt

Network Working Group                                   J. Gregorio, Ed.
Request for Comments: 5023                                        Google
Category: Standards Track                                B. de hOra, Ed.
                                                         NewBay Software
                                                            October 2007


                      The Atom Publishing Protocol

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   The Atom Publishing Protocol (AtomPub) is an application-level
   protocol for publishing and editing Web resources.  The protocol is
   based on HTTP transfer of Atom-formatted representations.  The Atom
   format is documented in the Atom Syndication Format.




























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Table of Contents

   1. Introduction ....................................................4
   2. Notational Conventions ..........................................4
      2.1. XML-Related Conventions ....................................4
           2.1.1. Referring to Information Items ......................4
           2.1.2. RELAX NG Schema .....................................4
           2.1.3. Use of "xml:base" and "xml:lang" ....................5
   3. Terminology .....................................................5
   4. Protocol Model ..................................................6
      4.1. Identity and Naming ........................................6
      4.2. Documents and Resource Classification ......................7
      4.3. Control and Publishing .....................................8
      4.4. Client Implementation Considerations .......................9
   5. Protocol Operations .............................................9
      5.1. Retrieving a Service Document .............................10
      5.2. Listing Collection Members ................................10
      5.3. Creating a Resource .......................................11
      5.4. Editing a Resource ........................................11
           5.4.1. Retrieving a Resource ..............................11
           5.4.2. Editing a Resource .................................12
           5.4.3. Deleting a Resource ................................12
      5.5. Use of HTTP Response Codes ................................12
   6. Protocol Documents .............................................13
      6.1. Document Types ............................................13
      6.2. Document Extensibility ....................................13
   7. Category Documents .............................................14
      7.1. Example ...................................................14
      7.2. Element Definitions .......................................14
           7.2.1. The "app:categories" Element .......................14
   8. Service Documents ..............................................15
      8.1. Workspaces ................................................16
      8.2. Example ...................................................16
      8.3. Element Definitions .......................................17
           8.3.1. The "app:service" Element ..........................17
           8.3.2. The "app:workspace" Element ........................18
           8.3.3. The "app:collection" Element .......................18
           8.3.4. The "app:accept" Element ...........................19
           8.3.5. Usage in Atom Feed Documents .......................19
           8.3.6. The "app:categories" Element .......................20
   9. Creating and Editing Resources .................................20
      9.1. Member URIs ...............................................20
      9.2. Creating Resources with POST ..............................20
           9.2.1. Example ............................................21
      9.3. Editing Resources with PUT ................................22
      9.4. Deleting Resources with DELETE ............................22
      9.5. Caching and Entity Tags ...................................22
           9.5.1. Example ............................................23



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      9.6. Media Resources and Media Link Entries ....................25
           9.6.1. Examples ...........................................26
      9.7. The Slug Header ...........................................30
           9.7.1. Slug Header Syntax .................................31
           9.7.2. Example ............................................31
   10. Listing Collections ...........................................32
      10.1. Collection Partial Lists .................................32
      10.2. The "app:edited" Element .................................33
   11. Atom Format Link Relation Extensions ..........................34
      11.1. The "edit" Link Relation .................................34
      11.2. The "edit-media" Link Relation ...........................34
   12. The Atom Format Type Parameter ................................34
      12.1. The "type" parameter .....................................34
           12.1.1. Conformance .......................................35
   13. Atom Publishing Controls ......................................35
      13.1. The "app:control" Element ................................35
           13.1.1. The "app:draft" Element ...........................36
   14. Securing the Atom Publishing Protocol .........................36
   15. Security Considerations .......................................37
      15.1. Denial of Service ........................................37
      15.2. Replay Attacks ...........................................37
      15.3. Spoofing Attacks .........................................37
      15.4. Linked Resources .........................................38
      15.5. Digital Signatures and Encryption ........................38
      15.6. URIs and IRIs ............................................38
      15.7. Code Injection and Cross Site Scripting ..................39
   16. IANA Considerations ...........................................39
      16.1. Content-Type Registration for 'application/atomcat+xml' ..39
      16.2. Content-Type Registration for 'application/atomsvc+xml' ..40
      16.3. Header Field Registration for 'SLUG' .....................42
      16.4. The Link Relation Registration "edit" ....................42
      16.5. The Link Relation Registration "edit-media" ..............42
      16.6. The Atom Format Media Type Parameter .....................43
   17. References ....................................................43
      17.1. Normative References .....................................43
      17.2. Informative References ...................................44
   Appendix A. Contributors ..........................................46
   Appendix B. RELAX NG Compact Schema ...............................46













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1.  Introduction

   The Atom Publishing Protocol is an application-level protocol for
   publishing and editing Web Resources using HTTP [RFC2616] and XML 1.0
   [REC-xml].  The protocol supports the creation of Web Resources and
   provides facilities for:

   o  Collections: Sets of Resources, which can be retrieved in whole or
      in part.

   o  Services: Discovery and description of Collections.

   o  Editing: Creating, editing, and deleting Resources.

   The Atom Publishing Protocol is different from many contemporary
   protocols in that the server is given wide latitude in processing
   requests from clients.  See Section 4.4 for more details.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.1.  XML-Related Conventions

2.1.1.  Referring to Information Items

   Atom Protocol Document formats are specified in terms of the XML
   Information Set [REC-xml-infoset], serialized as XML 1.0 [REC-xml].

   The Infoset terms "Element Information Item" and "Attribute
   Information Item" are shortened to "element" and "attribute"
   respectively.  Therefore, when this specification uses the term
   "element", it is referring to an Element Information Item, and when
   it uses the term "attribute", it is referring to an Attribute
   Information Item.

2.1.2.  RELAX NG Schema

   Some sections of this specification are illustrated with fragments of
   a non-normative RELAX NG Compact schema [RNC].  However, the text of
   this specification provides the definition of conformance.  Complete
   schemas appear in Appendix B.







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2.1.3.  Use of "xml:base" and "xml:lang"

   XML elements defined by this specification MAY have an "xml:base"
   attribute [REC-xmlbase].  When xml:base is used, it serves the
   function described in Section 5.1.1 of URI Generic Syntax [RFC3986],
   by establishing the base URI (or IRI, Internationalized Resource
   Identifier [RFC3987]) for resolving relative references found within
   the scope of the "xml:base" attribute.

   Any element defined by this specification MAY have an "xml:lang"
   attribute, whose content indicates the natural language for the
   element and its descendants.  Requirements regarding the content and
   interpretation of "xml:lang" are specified in Section 2.12 of XML 1.0
   [REC-xml].

3.  Terminology

   For convenience, this protocol can be referred to as the "Atom
   Protocol" or "AtomPub".  The following terminology is used by this
   specification:

   o  URI - A Uniform Resource Identifier as defined in [RFC3986].  In
      this specification, the phrase "the URI of a document" is
      shorthand for "a URI which, when dereferenced, is expected to
      produce that document as a representation".

   o  IRI - An Internationalized Resource Identifier as defined in
      [RFC3987].  Before an IRI found in a document is used by HTTP, the
      IRI is first converted to a URI.  See Section 4.1.

   o  Resource - A network-accessible data object or service identified
      by an IRI, as defined in [RFC2616].  See [REC-webarch] for further
      discussion on Resources.

   o  relation (or "relation of") - Refers to the "rel" attribute value
      of an atom:link element.

   o  Representation - An entity included with a request or response as
      defined in [RFC2616].

   o  Collection - A Resource that contains a set of Member Resources.
      Collections are represented as Atom Feeds.  See Section 9.









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   o  Member (or Member Resource) - A Resource whose IRI is listed in a
      Collection by an atom:link element with a relation of "edit" or
      "edit-media".  See Section 9.1.  The protocol defines two kinds of
      Members:

      *  Entry Resource - Members of a Collection that are represented
         as Atom Entry Documents, as defined in [RFC4287].

      *  Media Resource - Members of a Collection that have
         representations other than Atom Entry Documents.

   o  Media Link Entry - An Entry Resource that contains metadata about
      a Media Resource.  See Section 9.6.

   o  Workspace - A named group of Collections.  See Section 8.1.

   o  Service Document - A document that describes the location and
      capabilities of one or more Collections, grouped into Workspaces.
      See Section 8.

   o  Category Document - A document that describes the categories
      allowed in a Collection.  See Section 7.

4.  Protocol Model

   The Atom Protocol specifies operations for publishing and editing
   Resources using HTTP.  It uses Atom-formatted representations to
   describe the state and metadata of those Resources.  It defines how
   Collections of Resources can be organized, and it specifies formats
   to support their discovery, grouping and categorization.

4.1.  Identity and Naming

   Atom Protocol documents allow the use of IRIs [RFC3987] as well as
   URIs [RFC3986] to identify Resources.  Before an IRI in a document is
   used by HTTP, the IRI is first converted to a URI according to the
   procedure defined in Section 3.1 of [RFC3987].  In accordance with
   that specification, the conversion SHOULD be applied as late as
   possible.  Conversion does not imply Resource creation -- the IRI and
   the URI into which it is converted identify the same Resource.

   While the Atom Protocol specifies the formats of the representations
   that are exchanged and the actions that can be performed on the IRIs
   embedded in those representations, it does not constrain the form of
   the URIs that are used.  HTTP [RFC2616] specifies that the URI space
   of each server is controlled by that server, and this protocol
   imposes no further constraints on that control.




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4.2.  Documents and Resource Classification

   A Resource whose IRI is listed in a Collection is called a Member
   Resource.  The protocol defines two kinds of Member Resources --
   Entry Resources and Media Resources.  Entry Resources are represented
   as Atom Entry Documents [RFC4287].  Media Resources can have
   representations in any media type.  A Media Resource is described
   within a Collection using an Entry called a Media Link Entry.  This
   diagram shows the classification of Resources within the Atom
   Protocol:

                Member Resources
                       |
                -----------------
               |                 |
         Entry Resources     Media Resources
               |
         Media Link Entry

   The Atom Protocol defines Collection Resources for managing and
   organizing both kinds of Member Resource.  A Collection is
   represented by an Atom Feed Document.  A Collection Feed's Entries
   contain the IRIs of, and metadata about, the Collection's Member
   Resources.  A Collection Feed can contain any number of Entries,
   which might represent all the Members of the Collection, or an
   ordered subset of them (see Section 10.1).  In the diagram of a
   Collection below, there are two Entries.  The first contains the IRI
   of an Entry Resource.  The second contains the IRIs of both a Media
   Resource and a Media Link Entry, which contains the metadata for that
   Media Resource:

     Collection
        |
        o- Entry
        |    |
        |    o- Member Entry IRI (Entry Resource)
        |
        o- Entry
             |
             o- Member Entry IRI (Media Link Entry)
             |
             o- Media IRI        (Media Resource)

   The Atom Protocol does not make a distinction between Feeds used for
   Collections and other Atom Feeds.  The only mechanism that this
   specification supplies for indicating that a Feed is a Collection
   Feed is the presence of the Feed's IRI in a Service Document.




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   Service Documents represent server-defined groups of Collections, and
   are used to initialize the process of creating and editing Resources.
   These groups of Collections are called Workspaces.  Workspaces have
   names, but no IRIs, and no specified processing model.  The Service
   Document can indicate which media types, and which categories, a
   Collection will accept.  In the diagram below, there are two
   Workspaces each describing the IRIs, acceptable media types, and
   categories for a Collection:

     Service
        o- Workspace
        |    |
        |    o- Collection
        |         |
        |         o- IRI, categories, media types
        |
        o- Workspace
             |
             o- Collection
                  |
                  o- IRI, categories, media types

4.3.  Control and Publishing

   The Atom Publishing Protocol uses HTTP methods to author Member
   Resources as follows:

   o  GET is used to retrieve a representation of a known Resource.

   o  POST is used to create a new, dynamically named, Resource.  When
      the client submits non-Atom-Entry representations to a Collection
      for creation, two Resources are always created -- a Media Entry
      for the requested Resource, and a Media Link Entry for metadata
      about the Resource that will appear in the Collection.

   o  PUT is used to edit a known Resource.  It is not used for Resource
      creation.

   o  DELETE is used to remove a known Resource.

   The Atom Protocol only covers the creating, editing, and deleting of
   Entry and Media Resources.  Other Resources could be created, edited,
   and deleted as the result of manipulating a Collection, but the
   number of those Resources, their media types, and effects of Atom
   Protocol operations on them are outside the scope of this
   specification.





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   Since all aspects of client-server interaction are defined in terms
   of HTTP, [RFC2616] should be consulted for any areas not covered in
   this specification.

4.4.  Client Implementation Considerations

   The Atom Protocol imposes few restrictions on the actions of servers.
   Unless a constraint is specified here, servers can be expected to
   vary in behavior, in particular around the manipulation of Atom
   Entries sent by clients.  For example, although this specification
   only defines the expected behavior of Collections with respect to GET
   and POST, this does not imply that PUT, DELETE, PROPPATCH, and others
   are forbidden on Collection Resources -- only that this specification
   does not define what the server's response would be to those methods.
   Similarly, while some HTTP status codes are mentioned explicitly,
   clients ought to be prepared to handle any status code from a server.
   Servers can choose to accept, reject, delay, moderate, censor,
   reformat, translate, relocate, or re-categorize the content submitted
   to them.  Only some of these choices are immediately relayed back to
   the client in responses to client requests; other choices may only
   become apparent later, in the feed or published entries.  The same
   series of requests to two different publishing sites can result in a
   different series of HTTP responses, different resulting feeds, or
   different entry contents.

   As a result, client software has to be written flexibly to accept
   what the server decides are the results of its submissions.  Any
   server response or server content modification not explicitly
   forbidden by this specification or HTTP [RFC2616] is therefore
   allowed.

5.  Protocol Operations

   While specific HTTP status codes are shown in the interaction
   diagrams below, an AtomPub client should be prepared to handle any
   status code.  For example, a PUT to a Member URI could result in the
   return of a "204 No Content" status code, which still indicates
   success.













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5.1.  Retrieving a Service Document

   Client                                     Server
     |                                           |
     |  1.) GET to Service Document URI          |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 Ok                               |
     |      Service Document                     |
     |<------------------------------------------|
     |                                           |

   1.  The client sends a GET request to the URI of the Service
       Document.

   2.  The server responds with a Service Document enumerating the IRIs
       of a group of Collections and the capabilities of those
       Collections supported by the server.  The content of this
       document can vary based on aspects of the client request,
       including, but not limited to, authentication credentials.

5.2.  Listing Collection Members

   To list the Members of a Collection, the client sends a GET request
   to the URI of a Collection.  An Atom Feed Document is returned whose
   Entries contain the IRIs of Member Resources.  The returned Feed may
   describe all, or only a partial list, of the Members in a Collection
   (see Section 10).

   Client                          Server
     |                                |
     |  1.) GET to Collection URI     |
     |------------------------------->|
     |                                |
     |  2.) 200 Ok                    |
     |      Atom Feed Document        |
     |<-------------------------------|
     |                                |

   1.  The client sends a GET request to the URI of the Collection.

   2.  The server responds with an Atom Feed Document containing the
       IRIs of the Collection Members.








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5.3.  Creating a Resource

   Client                                     Server
     |                                           |
     |  1.) POST to Collection URI               |
     |      Member Representation                |
     |------------------------------------------>|
     |                                           |
     |  2.) 201 Created                          |
     |      Location: Member Entry URI           |
     |<------------------------------------------|
     |                                           |

   1.  The client POSTs a representation of the Member to the URI of the
       Collection.

   2.  If the Member Resource was created successfully, the server
       responds with a status code of 201 and a Location header that
       contains the IRI of the newly created Entry Resource.  Media
       Resources could have also been created and their IRIs can be
       found through the Entry Resource.  See Section 9.6 for more
       details.

5.4.  Editing a Resource

   Once a Resource has been created and its Member URI is known, that
   URI can be used to retrieve, edit, and delete the Resource.  Section
   11 describes extensions to the Atom Syndication Format used in the
   Atom Protocol for editing purposes.

5.4.1.  Retrieving a Resource

   Client                                     Server
     |                                           |
     |  1.) GET to Member URI                    |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 Ok                               |
     |      Member Representation                |
     |<------------------------------------------|
     |                                           |

   1.  The client sends a GET request to the URI of a Member Resource to
       retrieve its representation.

   2.  The server responds with the representation of the Member
       Resource.




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5.4.2.  Editing a Resource

   Client                                     Server
     |                                           |
     |  1.) PUT to Member URI                    |
     |      Member Representation                |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 OK                               |
     |<------------------------------------------|

   1.  The client sends a PUT request to store a representation of a
       Member Resource.

   2.  If the request is successful, the server responds with a status
       code of 200.

5.4.3.  Deleting a Resource

   Client                                     Server
     |                                           |
     |  1.) DELETE to Member URI                 |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 OK                               |
     |<------------------------------------------|
     |                                           |

   1.  The client sends a DELETE request to the URI of a Member
       Resource.

   2.  If the deletion is successful, the server responds with a status
       code of 200.

   A different approach is taken for deleting Media Resources; see
   Section 9.4 for details.

5.5.  Use of HTTP Response Codes

   The Atom Protocol uses the response status codes defined in HTTP to
   indicate the success or failure of an operation.  Consult the HTTP
   specification [RFC2616] for detailed definitions of each status code.

   Implementers are asked to note that according to the HTTP
   specification, HTTP 4xx and 5xx response entities SHOULD include a
   human-readable explanation of the error.





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6.  Protocol Documents

6.1.  Document Types

   This specification defines two kinds of documents -- Category
   Documents and Service Documents.

   A Category Document (Section 7) contains lists of categories
   specified using the "atom:category" element from the Atom Syndication
   Format (see Section 4.2.2 of [RFC4287]).

   A Service Document (Section 8) groups available Collections into
   Workspaces.

   The namespace name [REC-xml-names] for either kind of document is:

       http://www.w3.org/2007/app

   Atom Publishing Protocol XML Documents MUST be "namespace-well-
   formed" as specified in Section 7 of [REC-xml-names].

   This specification uses the prefix "app:" for the namespace name.
   The prefix "atom:" is used for "http://www.w3.org/2005/Atom", the
   namespace name of the Atom Syndication Format [RFC4287].  These
   namespace prefixes are not semantically significant.

   This specification does not define any DTDs for Atom Protocol
   formats, and hence does not require them to be "valid" in the sense
   used by [REC-xml].

6.2.  Document Extensibility

   Unrecognized markup in an Atom Publishing Protocol document is
   considered "foreign markup" as defined in Section 6 of the Atom
   Syndication Format [RFC4287].  Foreign markup can be used anywhere
   within a Category or Service Document unless it is explicitly
   forbidden.  Processors that encounter foreign markup MUST NOT stop
   processing and MUST NOT signal an error.  Clients SHOULD preserve
   foreign markup when transmitting such documents.

   The namespace name "http://www.w3.org/2007/app" is reserved for
   forward-compatible revisions of the Category and Service Document
   types.  This does not exclude the addition of elements and attributes
   that might not be recognized by processors conformant to this
   specification.  Such unrecognized markup from the
   "http://www.w3.org/2007/app" namespace MUST be treated as foreign
   markup.




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7.  Category Documents

   Category Documents contain lists of categories described using the
   "atom:category" element from the Atom Syndication Format [RFC4287].
   Categories can also appear in Service Documents, where they indicate
   the categories allowed in a Collection (see Section 8.3.6).

   Category Documents are identified with the "application/atomcat+xml"
   media type (see Section 16.1).

7.1.  Example

       <?xml version="1.0" ?>
       <app:categories
           xmlns:app="http://www.w3.org/2007/app"
           xmlns:atom="http://www.w3.org/2005/Atom"
           fixed="yes" scheme="http://example.com/cats/big3">
         <atom:category term="animal" />
         <atom:category term="vegetable" />
         <atom:category term="mineral" />
       </app:categories>

   This Category Document contains atom:category elements, with the
   terms 'animal', 'vegetable', and 'mineral'.  None of the categories
   use the "label" attribute defined in [RFC4287].  They all inherit the
   "http://example.com/cats/big3" "scheme" attribute declared on the
   app:categories element.  Therefore if the 'mineral' category were to
   appear in an Atom Entry or Feed Document, it would appear as:

   <atom:category scheme="http://example.com/cats/big3" term="mineral"/>

7.2.  Element Definitions

7.2.1.  The "app:categories" Element

   The root of a Category Document is the "app:categories" element.  An
   app:categories element can contain zero or more atom:category
   elements from the Atom Syndication Format [RFC4287] namespace
   ("http://www.w3.org/2005/Atom").

   An atom:category child element that has no "scheme" attribute
   inherits the attribute from its app:categories parent.  An atom:
   category child element with an existing "scheme" attribute does not
   inherit the "scheme" value of its app:categories parent element.







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   atomCategory =
       element atom:category {
          atomCommonAttributes,
          attribute term { text },
          attribute scheme { atomURI }?,
          attribute label { text }?,
          undefinedContent
       }

   appInlineCategories =
       element app:categories {
           attribute fixed { "yes" | "no" }?,
           attribute scheme { atomURI }?,
           (atomCategory*,
           undefinedContent)
       }

   appOutOfLineCategories =
       element app:categories {
           attribute href { atomURI },
           undefinedContent
       }

   appCategories = appInlineCategories | appOutOfLineCategories

7.2.1.1.  Attributes of "app:categories"

   The app:categories element can contain a "fixed" attribute, with a
   value of either "yes" or "no", indicating whether the list of
   categories is a fixed or an open set.  The absence of the "fixed"
   attribute is equivalent to the presence of a "fixed" attribute with a
   value of "no".

   Alternatively, the app:categories element MAY contain an "href"
   attribute, whose value MUST be an IRI reference identifying a
   Category Document.  If the "href" attribute is provided, the app:
   categories element MUST be empty and MUST NOT have the "fixed" or
   "scheme" attributes.

8.  Service Documents

   For authoring to commence, a client needs to discover the
   capabilities and locations of the available Collections.  Service
   Documents are designed to support this discovery process.

   How Service Documents are discovered is not defined in this
   specification.




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   Service Documents are identified with the "application/atomsvc+xml"
   media type (see Section 16.2).

8.1.  Workspaces

   A Service Document groups Collections into Workspaces.  Operations on
   Workspaces, such as creation or deletion, are not defined by this
   specification.  This specification assigns no meaning to Workspaces;
   that is, a Workspace does not imply any specific processing
   assumptions.

   There is no requirement that a server support multiple Workspaces.
   In addition, a Collection MAY appear in more than one Workspace.

8.2.  Example

   <?xml version="1.0" encoding='utf-8'?>
   <service xmlns="http://www.w3.org/2007/app"
            xmlns:atom="http://www.w3.org/2005/Atom">
     <workspace>
       <atom:title>Main Site</atom:title>
       <collection
           href="http://example.org/blog/main" >
         <atom:title>My Blog Entries</atom:title>
         <categories
            href="http://example.com/cats/forMain.cats" />
       </collection>
       <collection
           href="http://example.org/blog/pic" >
         <atom:title>Pictures</atom:title>
         <accept>image/png</accept>
         <accept>image/jpeg</accept>
         <accept>image/gif</accept>
       </collection>
     </workspace>
     <workspace>
       <atom:title>Sidebar Blog</atom:title>
       <collection
           href="http://example.org/sidebar/list" >
         <atom:title>Remaindered Links</atom:title>
         <accept>application/atom+xml;type=entry</accept>
         <categories fixed="yes">
           <atom:category
             scheme="http://example.org/extra-cats/"
             term="joke" />
           <atom:category
             scheme="http://example.org/extra-cats/"
             term="serious" />



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         </categories>
       </collection>
     </workspace>
   </service>

   The Service Document above describes two Workspaces.  The first
   Workspace is called "Main Site", and has two Collections called "My
   Blog Entries" and "Pictures", whose IRIs are
   "http://example.org/blog/main" and "http://example.org/blog/pic"
   respectively.  The "Pictures" Collection includes three "accept"
   elements indicating the types of image files the client can send to
   the Collection to create new Media Resources (entries associated with
   Media Resources are discussed in Section 9.6).

   The second Workspace is called "Sidebar Blog" and has a single
   Collection called "Remaindered Links" whose IRI is
   "http://example.org/sidebar/list".  The Collection has an "accept"
   element whose content is "application/atom+xml;type=entry",
   indicating it will accept Atom Entries from a client.

   Within each of the two Entry Collections, the "categories" element
   provides a list of available categories for Member Entries.  In the
   "My Blog Entries" Collection, the list of available categories is
   available through the "href" attribute.  The "Sidebar Blog"
   Collection provides a category list within the Service Document, but
   states the list is fixed, signaling a request from the server that
   Entries be POSTed using only those two categories.

8.3.  Element Definitions

8.3.1.  The "app:service" Element

   The root of a Service Document is the "app:service" element.

   The app:service element is the container for service information
   associated with one or more Workspaces.  An app:service element MUST
   contain one or more app:workspace elements.

   namespace app = "http://www.w3.org/2007/app"
   start = appService

   appService =
      element app:service {
         appCommonAttributes,
         ( appWorkspace+
           & extensionElement* )
      }




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8.3.2.  The "app:workspace" Element

   Workspaces are server-defined groups of Collections.  The "app:
   workspace" element contains zero or more app:collection elements
   describing the Collections of Resources available for editing.

   appWorkspace =
      element app:workspace {
         appCommonAttributes,
         ( atomTitle
           & appCollection*
           & extensionSansTitleElement* )
      }

   atomTitle = element atom:title { atomTextConstruct }

8.3.2.1.  The "atom:title" Element

   The app:workspace element MUST contain one "atom:title" element (as
   defined in [RFC4287]), giving a human-readable title for the
   Workspace.

8.3.3.  The "app:collection" Element

   The "app:collection" element describes a Collection.  The app:
   collection element MUST contain one atom:title element.

   The app:collection element MAY contain any number of app:accept
   elements, indicating the types of representations accepted by the
   Collection.  The order of such elements is not significant.

   The app:collection element MAY contain any number of app:categories
   elements.

   appCollection =
      element app:collection {
         appCommonAttributes,
         attribute href { atomURI  },
         ( atomTitle
           & appAccept*
           & appCategories*
           & extensionSansTitleElement* )
      }

8.3.3.1.  The "href" Attribute

   The app:collection element MUST contain an "href" attribute, whose
   value gives the IRI of the Collection.



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8.3.3.2.  The "atom:title" Element

   The "atom:title" element is defined in [RFC4287] and gives a human-
   readable title for the Collection.

8.3.4.  The "app:accept" Element

   The content of an "app:accept" element value is a media range as
   defined in [RFC2616].  The media range specifies a type of
   representation that can be POSTed to a Collection.

   The app:accept element is similar to the HTTP Accept request-header
   [RFC2616].  Media type parameters are allowed within app:accept, but
   app:accept has no notion of preference -- "accept-params" or "q"
   arguments, as specified in Section 14.1 of [RFC2616] are not
   significant.

   White space (as defined in [REC-xml]) around the app:accept element's
   media range is insignificant and MUST be ignored.

   A value of "application/atom+xml;type=entry" MAY appear in any app:
   accept list of media ranges and indicates that Atom Entry Documents
   can be POSTed to the Collection.  If no app:accept element is
   present, clients SHOULD treat this as equivalent to an app:accept
   element with the content "application/atom+xml;type=entry".

   If one app:accept element exists and is empty, clients SHOULD assume
   that the Collection does not support the creation of new Entries.

   appAccept =
      element app:accept {
            appCommonAttributes,
            ( text? )
      }

8.3.5.  Usage in Atom Feed Documents

   The app:collection element MAY appear as a child of an atom:feed or
   atom:source element in an Atom Feed Document.  Its content identifies
   a Collection by which new Entries can be added to appear in the feed.
   When it appears in an atom:feed or atom:source element, the app:
   collection element is considered foreign markup as defined in Section
   6 of [RFC4287].








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8.3.6.  The "app:categories" Element

   The "app:categories" element provides a list of the categories that
   can be applied to the members of a Collection.  See Section 7.2.1 for
   the detailed definition of app:categories.

   The server MAY reject attempts to create or store members whose
   categories are not present in its categories list.  A Collection that
   indicates the category set is open SHOULD NOT reject otherwise
   acceptable members whose categories are not in its categories list.
   The absence of an app:categories element means that the category
   handling of the Collection is unspecified.  A "fixed" category list
   that contains zero categories indicates the Collection does not
   accept category data.

9.  Creating and Editing Resources

9.1.  Member URIs

   The Member URI allows clients to retrieve, edit, and delete a Member
   Resource using HTTP's GET, PUT, and DELETE methods.  Entry Resources
   are represented as Atom Entry documents.

   Member URIs appear in two places.  They are returned in a Location
   header after successful Resource creation using POST, as described in
   Section 9.2 below.  They can also appear in a Collection Feed's
   Entries, as atom:link elements with a link relation of "edit".

   A Member Entry SHOULD contain such an atom:link element with a link
   relation of "edit", which indicates the Member URI.

9.2.  Creating Resources with POST

   To add members to a Collection, clients send POST requests to the URI
   of the Collection.

   Successful member creation is indicated with a 201 ("Created")
   response code.  When the Collection responds with a status code of
   201, it SHOULD also return a response body, which MUST be an Atom
   Entry Document representing the newly created Resource.  Since the
   server is free to alter the POSTed Entry, for example, by changing
   the content of the atom:id element, returning the Entry can be useful
   to the client, enabling it to correlate the client and server views
   of the new Entry.

   When a Member Resource is created, its Member Entry URI MUST be
   returned in a Location header in the Collection's response.




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   If the creation request contained an Atom Entry Document, and the
   subsequent response from the server contains a Content-Location
   header that matches the Location header character-for-character, then
   the client is authorized to interpret the response entity as being a
   complete representation of the newly created Entry.  Without a
   matching Content-Location header, the client MUST NOT assume the
   returned entity is a complete representation of the created Resource.

   The request body sent with the POST need not be an Atom Entry.  For
   example, it might be a picture or a movie.  Collections MAY return a
   response with a status code of 415 ("Unsupported Media Type") to
   indicate that the media type of the POSTed entity is not allowed or
   supported by the Collection.  For a discussion of the issues in
   creating such content, see Section 9.6.

9.2.1.  Example

   Below, the client sends a POST request containing an Atom Entry
   representation using the URI of the Collection:

       POST /edit/ HTTP/1.1
       Host: example.org
       User-Agent: Thingio/1.0
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Type: application/atom+xml;type=entry
       Content-Length: nnn
       Slug: First Post

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>Atom-Powered Robots Run Amok</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2003-12-13T18:30:02Z</updated>
         <author><name>John Doe</name></author>
         <content>Some text.</content>
       </entry>

   The server signals a successful creation with a status code of 201.
   The response includes a Location header indicating the Member Entry
   URI of the Atom Entry, and a representation of that Entry in the body
   of the response.

       HTTP/1.1 201 Created
       Date: Fri, 7 Oct 2005 17:17:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry;charset="utf-8"
       Location: http://example.org/edit/first-post.atom
       ETag: "c180de84f991g8"



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       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>Atom-Powered Robots Run Amok</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2003-12-13T18:30:02Z</updated>
         <author><name>John Doe</name></author>
         <content>Some text.</content>
         <link rel="edit"
             href="http://example.org/edit/first-post.atom"/>
       </entry>

   The Entry created and returned by the Collection might not match the
   Entry POSTed by the client.  A server MAY change the values of
   various elements in the Entry, such as the atom:id, atom:updated, and
   atom:author values, and MAY choose to remove or add other elements
   and attributes, or change element content and attribute values.

9.3.  Editing Resources with PUT

   To edit a Member Resource, a client sends a PUT request to its Member
   URI, as specified in [RFC2616].

   To avoid unintentional loss of data when editing Member Entries or
   Media Link Entries, an Atom Protocol client SHOULD preserve all
   metadata that has not been intentionally modified, including unknown
   foreign markup as defined in Section 6 of [RFC4287].

9.4.  Deleting Resources with DELETE

   To delete a Member Resource, a client sends a DELETE request to its
   Member URI, as specified in [RFC2616].  The deletion of a Media Link
   Entry SHOULD result in the deletion of the corresponding Media
   Resource.

9.5.  Caching and Entity Tags

   Implementers are advised to pay attention to cache controls and to
   make use of the mechanisms available in HTTP when editing Resources,
   in particular, entity-tags as outlined in [NOTE-detect-lost-update].
   Clients are not assured to receive the most recent representations of
   Collection Members using GET if the server is authorizing
   intermediaries to cache them.









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9.5.1.  Example

   Below, the client creates a Member Entry using POST:

       POST /myblog/entries HTTP/1.1
       Host: example.org
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Type: application/atom+xml;type=entry
       Content-Length: nnn
       Slug: First Post

       <?xml version="1.0" ?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>Atom-Powered Robots Run Amok</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2007-02-123T17:09:02Z</updated>
         <author><name>Captain Lansing</name></author>
         <content>It's something moving... solid metal</content>
       </entry>

   The server signals a successful creation with a status code of 201,
   and returns an ETag header in the response.  Because, in this case,
   the server returned a Content-Location header and Location header
   with the same value, the returned Entry representation can be
   understood to be a complete representation of the newly created Entry
   (see Section 9.2).

       HTTP/1.1 201 Created
       Date: Fri, 23 Feb 2007 21:17:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry
       Location: http://example.org/edit/first-post.atom
       Content-Location: http://example.org/edit/first-post.atom
       ETag: "e180ee84f0671b1"

       <?xml version="1.0" ?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>Atom-Powered Robots Run Amok</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2007-02-123T17:09:02Z</updated>
         <author><name>Captain Lansing</name></author>
         <content>It's something moving... solid metal</content>
       </entry>

   The client can, if it wishes, use the returned ETag value to later
   construct a "Conditional GET" as defined in [RFC2616].  In this case,
   prior to editing, the client sends the ETag value for the Member
   using the If-None-Match header.



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       GET /edit/first-post.atom HTTP/1.1
       Host: example.org
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       If-None-Match: "e180ee84f0671b1"

   If the Entry has not been modified, the response will be a status
   code of 304 ("Not Modified").  This allows the client to determine
   whether it still has the most recent representation of the Entry at
   the time of editing.

       HTTP/1.1 304 Not Modified
       Date: Sat, 24 Feb 2007 13:17:11 GMT

   After editing, the client can PUT the Entry and send the ETag entity
   value in an If-Match header, informing the server to accept the entry
   on the condition that the entity value sent still matches the
   server's.

       PUT /edit/first-post.atom HTTP/1.1
       Host: example.org
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Type: application/atom+xml;type=entry
       Content-Length: nnn
       If-Match: "e180ee84f0671b1"

       <?xml version="1.0" ?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>Atom-Powered Robots Run Amok</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2007-02-24T16:34:06Z</updated>
         <author><name>Captain Lansing</name></author>
         <content>Update: it's a hoax!</content>
       </entry>

   The server however has since received a more recent copy than the
   client's, and it responds with a status code of 412 ("Precondition
   Failed").

       HTTP/1.1 412 Precondition Failed
       Date: Sat, 24 Feb 2007 16:34:11 GMT

   This informs the client that the server has a more recent version of
   the Entry and will not allow the sent entity to be stored.








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9.6.  Media Resources and Media Link Entries

   A client can POST Media Resources as well as Entry Resources to a
   Collection.  If a server accepts such a request, then it MUST create
   two new Resources -- one that corresponds to the entity sent in the
   request, called the Media Resource, and an associated Member Entry,
   called the Media Link Entry.  Media Link Entries are represented as
   Atom Entries, and appear in the Collection.

   The Media Link Entry contains the metadata and IRI of the (perhaps
   non-textual) Media Resource.  The Media Link Entry thus makes the
   metadata about the Media Resource separately available for retrieval
   and alteration.

   The server can signal the media types it will accept using the app:
   accept element in the Service Document, as specified in Section
   8.3.4.

   Successful responses to creation requests MUST include the URI of the
   Media Link Entry in the Location header.  The Media Link Entry SHOULD
   contain an atom:link element with a link relation of "edit-media"
   that contains the Media Resource IRI.  The Media Link Entry MUST have
   an atom:content element with a "src" attribute.  The value of the
   "src" attribute is an IRI for the newly created Media Resource.  It
   is OPTIONAL that the IRI of the "src" attribute on the atom:content
   element be the same as the Media Resource IRI.  For example, the
   "src" attribute value might instead be a link into a static cache or
   content distribution network and not the Media Resource IRI.

   Implementers are asked to note that [RFC4287] specifies that Atom
   Entries MUST contain an atom:summary element.  Thus, upon successful
   creation of a Media Link Entry, a server MAY choose to populate the
   atom:summary element (as well as any other mandatory elements such as
   atom:id, atom:author, and atom:title) with content derived from the
   POSTed entity or from any other source.  A server might not allow a
   client to modify the server-selected values for these elements.

   For Resource creation, this specification only defines cases where
   the POST body has an Atom Entry entity declared as an Atom media type
   ("application/atom+xml"), or a non-Atom entity declared as a non-Atom
   media type.  When a client is POSTing an Atom Entry to a Collection,
   it may use a media type of either "application/atom+xml" or
   "application/atom +xml;type=entry".  This specification does not
   specify any request semantics or server behavior in the case where
   the POSTed media type is "application/atom+xml" but the body is
   something other than an Atom Entry.  In particular, what happens on
   POSTing an Atom Feed Document to a Collection using the "application/
   atom+xml" media type is undefined.



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   The Atom Protocol does not specify a means to create multiple
   representations of the same Resource (for example, a PNG and a JPG of
   the same image) either on creation or editing.

9.6.1.  Examples

   Below, the client sends a POST request containing a PNG image to the
   URI of a Collection that accepts PNG images:

       POST /edit/ HTTP/1.1
       Host: media.example.org
       Content-Type: image/png
       Slug: The Beach
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Length: nnn

       ...binary data...

   The server signals a successful creation with a status code of 201.
   The response includes a Location header indicating the Member URI of
   the Media Link Entry and a representation of that entry in the body
   of the response.  The Media Link Entry includes a content element
   with a "src" attribute.  It also contains a link with a link relation
   of "edit-media", specifying the IRI to be used for modifying the
   Media Resource.

       HTTP/1.1 201 Created
       Date: Fri, 7 Oct 2005 17:17:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry;charset="utf-8"
       Location: http://example.org/media/edit/the_beach.atom

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>The Beach</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2005-10-07T17:17:08Z</updated>
         <author><name>Daffy</name></author>
         <summary type="text" />
         <content type="image/png"
            src="http://media.example.org/the_beach.png"/>
         <link rel="edit-media"
            href="http://media.example.org/edit/the_beach.png" />
         <link rel="edit"
            href="http://example.org/media/edit/the_beach.atom" />
       </entry>





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   Later, the client sends a PUT request containing the new PNG using
   the URI indicated in the Media Link Entry's "edit-media" link:

       PUT /edit/the_beach.png HTTP/1.1
       Host: media.example.org
       Content-Type: image/png
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Length: nnn

       ...binary data...

   The server signals a successful edit with a status code of 200.

       HTTP/1.1 200 Ok
       Date: Fri, 8 Oct 2006 17:17:11 GMT

   The client can edit the metadata for the picture.  First GET the
   Media Link Entry:

       GET /media/edit/the_beach.atom HTTP/1.1
       Host: example.org
       Authorization: Basic ZGFmZnk6c2VjZXJldA==

   The Media Link Entry is returned.

       HTTP/1.1 200 Ok
       Date: Fri, 7 Oct 2005 17:18:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry;charset="utf-8"
       ETag: "c181bb840673b5"

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>The Beach</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2005-10-07T17:17:08Z</updated>
         <author><name>Daffy</name></author>
         <summary type="text" />
         <content type="image/png"
            src="http://media.example.org/the_beach.png"/>
         <link rel="edit-media"
            href="http://media.example.org/edit/the_beach.png" />
         <link rel="edit"
            href="http://example.org/media/edit/the_beach.atom" />
       </entry>

   The metadata can be updated, in this case to add a summary, and then
   PUT back to the server.



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       PUT /media/edit/the_beach.atom HTTP/1.1
       Host: example.org
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Type: application/atom+xml;type=entry
       Content-Length: nnn
       If-Match: "c181bb840673b5"

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>The Beach</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
         <updated>2005-10-07T17:17:08Z</updated>
         <author><name>Daffy</name></author>
         <summary type="text">
             A nice sunset picture over the water.
         </summary>
         <content type="image/png"
            src="http://media.example.org/the_beach.png"/>
         <link rel="edit-media"
            href="http://media.example.org/edit/the_beach.png" />
         <link rel="edit"
            href="http://example.org/media/edit/the_beach.atom" />
       </entry>

   The update was successful.

       HTTP/1.1 200 Ok
       Date: Fri, 7 Oct 2005 17:19:11 GMT
       Content-Length: 0

   Multiple Media Resources can be added to the Collection.

       POST /edit/ HTTP/1.1
       Host: media.example.org
       Content-Type: image/png
       Slug: The Pier
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Length: nnn

       ...binary data...

   The Resource is created successfully.

       HTTP/1.1 201 Created
       Date: Fri, 7 Oct 2005 17:17:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry;charset="utf-8"
       Location: http://example.org/media/edit/the_pier.atom



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       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>The Pier</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efe6b</id>
         <updated>2005-10-07T17:26:43Z</updated>
         <author><name>Daffy</name></author>
         <summary type="text" />
         <content type="image/png"
            src="http://media.example.org/the_pier.png"/>
         <link rel="edit-media"
            href="http://media.example.org/edit/the_pier.png" />
         <link rel="edit"
            href="http://example.org/media/edit/the_pier.atom" />
       </entry>

   The client can now create a new Atom Entry in the blog Entry
   Collection that references the two newly created Media Resources.

       POST /blog/ HTTP/1.1
       Host: example.org
       Content-Type: application/atom+xml;type=entry
       Slug: A day at the beach
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Length: nnn

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>A fun day at the beach</title>
         <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6b</id>
         <updated>2005-10-07T17:40:02Z</updated>
         <author><name>Daffy</name></author>
         <content type="xhtml">
             <xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
                 <xhtml:p>We had a good day at the beach.
                     <xhtml:img alt="the beach"
                         src="http://media.example.org/the_beach.png"/>
                 </xhtml:p>
                 <xhtml:p>Later we walked down to the pier.
                     <xhtml:img  alt="the pier"
                         src="http://media.example.org/the_pier.png"/>
                 </xhtml:p>
             </xhtml:div>
         </content>
       </entry>

   The Resource is created successfully.





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       HTTP/1.1 200 Ok
       Date: Fri, 7 Oct 2005 17:20:11 GMT
       Content-Length: nnn
       Content-Type: application/atom+xml;type=entry;charset="utf-8"
       Location: http://example.org/blog/atom/a-day-at-the-beach.atom

       <?xml version="1.0"?>
       <entry xmlns="http://www.w3.org/2005/Atom">
         <title>A fun day at the beach</title>
         <id>http://example.org/blog/a-day-at-the-beach.xhtml</id>
         <updated>2005-10-07T17:43:07Z</updated>
         <author><name>Daffy</name></author>
         <content type="xhtml">
             <xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
                 <xhtml:p>We had a good day at the beach.
                     <xhtml:img alt="the beach"
                        src="http://media.example.org/the_beach.png"/>
                 </xhtml:p>
                 <xhtml:p>Later we walked down to the pier.
                     <xhtml:img alt="the pier"
                        src="http://media.example.org/the_pier.png"/>
                 </xhtml:p>
             </xhtml:div>
         </content>
         <link rel="edit"
           href="http://example.org/blog/edit/a-day-at-the-beach.atom"/>
         <link rel="alternate" type="text/html"
           href="http://example.org/blog/a-day-at-the-beach.html"/>
       </entry>

   Note that the returned Entry contains a link with a relation of
   "alternate" that points to the associated HTML page that was created
   -- this is not required by this specification, but is included to
   show the kinds of changes a server can make to an Entry.

9.7.  The Slug Header

   Slug is an HTTP entity-header whose presence in a POST to a
   Collection constitutes a request by the client to use the header's
   value as part of any URIs that would normally be used to retrieve the
   to-be-created Entry or Media Resources.

   Servers MAY use the value of the Slug header when creating the Member
   URI of the newly created Resource, for instance, by using some or all
   of the words in the value for the last URI segment.  Servers MAY also
   use the value when creating the atom:id, or as the title of a Media
   Link Entry (see Section 9.6).




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   Servers MAY choose to ignore the Slug entity-header.  Servers MAY
   alter the header value before using it.  For instance, a server might
   filter out some characters or replace accented letters with non-
   accented ones, replace spaces with underscores, change case, and so
   on.

9.7.1.  Slug Header Syntax

   The syntax of the Slug header is defined using the augmented BNF
   syntax defined in Section 2.1 of [RFC2616]:

       LWS      = <defined in Section 2.2 of [RFC2616]>
       slugtext = %x20-7E | LWS
       Slug     = "Slug" ":" *slugtext

   The field value is the percent-encoded value of the UTF-8 encoding of
   the character sequence to be included (see Section 2.1 of [RFC3986]
   for the definition of percent encoding, and [RFC3629] for the
   definition of the UTF-8 encoding).

   Implementation note: to produce the field value from a character
   sequence, first encode it using the UTF-8 encoding, then encode all
   octets outside the ranges %20-24 and %26-7E using percent encoding
   (%25 is the ASCII encoding of "%", thus it needs to be escaped).  To
   consume the field value, first reverse the percent encoding, then run
   the resulting octet sequence through a UTF-8 decoding process.

9.7.2.  Example

   Here is an example of the Slug header that uses percent-encoding to
   represent the Unicode character U+00E8 (LATIN SMALL LETTER E WITH
   GRAVE):

       POST /myblog/entries HTTP/1.1
       Host: example.org
       Content-Type: image/png
       Slug: The Beach at S%C3%A8te
       Authorization: Basic ZGFmZnk6c2VjZXJldA==
       Content-Length: nnn

       ...binary data...

   See Section 9.2.1 for an example of the Slug header applied to the
   creation of an Entry Resource.







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10.  Listing Collections

   Collection Resources MUST provide representations in the form of Atom
   Feed Documents whose Entries contain the IRIs of the Members in the
   Collection.  No distinction is made between Collection Feeds and
   other kinds of Feeds -- a Feed might act both as a 'public' feed for
   subscription purposes and as a Collection Feed.

   Each Entry in the Feed Document SHOULD have an atom:link element with
   a relation of "edit" (see Section 11.1).

   The Entries in the returned Atom Feed SHOULD be ordered by their
   "app:edited" property, with the most recently edited Entries coming
   first in the document order.  The app:edited value is not equivalent
   to the HTTP Last-Modified header and cannot be used to determine the
   freshness of cached responses.

   Clients MUST NOT assume that an Atom Entry returned in the Feed is a
   full representation of an Entry Resource and SHOULD perform a GET on
   the URI of the Member Entry before editing it.  See Section 9.5 for a
   discussion on the implications of cache control directives when
   obtaining entries.

10.1.  Collection Partial Lists

   Collections can contain large numbers of Resources.  A client such as
   a web spider or web browser might be overwhelmed if the response to a
   GET contained every Entry in a Collection -- in turn the server might
   also waste bandwidth and processing time on generating a response
   that cannot be handled.  For this reason, servers MAY respond to
   Collection GET requests with a Feed Document containing a partial
   list of the Collection's members, and a link to the next partial list
   feed, if it exists.  The first such partial list returned MUST
   contain the most recently edited member Resources and MUST have an
   atom:link with a "next" relation whose "href" value is the URI of the
   next partial list of the Collection.  This next partial list will
   contain the next most recently edited set of Member Resources (and an
   atom:link to the following partial list if it exists).

   In addition to the "next" relation, partial list feeds MAY contain
   link elements with "rel" attribute values of "previous", "first", and
   "last", that can be used to navigate through the complete set of
   entries in the Collection.

   For instance, suppose a client is supplied the URI
   "http://example.org/entries/go" of a Collection of Member Entries,
   where the server as a matter of policy avoids generating Feed
   Documents containing more than 10 Entries.  The Atom Feed Document



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   for the Collection will then represent the first partial list of a
   set of 10 linked Feed Documents.  The "first" relation references the
   initial Feed Document in the set and the "last" relation references
   the final Feed Document in the set.  Within each document, the
   "previous" and "next" link relations reference the preceding and
   subsequent documents.

     <feed xmlns="http://www.w3.org/2005/Atom">
       <link rel="first"
             href="http://example.org/entries/go" />
       <link rel="next"
             href="http://example.org/entries/2" />
       <link rel="last"
             href="http://example.org/entries/10" />
       ...
     </feed>

   The "previous" and "next" link elements for the partial list feed
   located at "http://example.org/entries/2" would look like this:

     <feed xmlns="http://www.w3.org/2005/Atom">
       <link rel="first"
             href="http://example.org/entries/go" />
       <link rel="previous"
             href="http://example.org/entries/go" />
       <link rel="next"
             href="http://example.org/entries/3" />
       <link rel="last"
             href="http://example.org/entries/10" />
       ...
     </feed>

10.2.  The "app:edited" Element

   The "app:edited" element is a Date construct (as defined by
   [RFC4287]), whose content indicates the last time an Entry was
   edited.  If the entry has not been edited yet, the content indicates
   the time it was created.  Atom Entry elements in Collection Documents
   SHOULD contain one app:edited element, and MUST NOT contain more than
   one.

   appEdited = element app:edited ( atomDateConstruct )

   The server SHOULD change the value of this element every time an
   Entry Resource or an associated Media Resource has been edited.






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11.  Atom Format Link Relation Extensions

11.1.  The "edit" Link Relation

   This specification adds the value "edit" to the Atom Registry of Link
   Relations (see Section 7.1 of [RFC4287]).  The value of "edit"
   specifies that the value of the href attribute is the IRI of an
   editable Member Entry.  When appearing within an atom:entry, the href
   IRI can be used to retrieve, update, and delete the Resource
   represented by that Entry.  An atom:entry MUST NOT contain more than
   one "edit" link relation.

11.2.  The "edit-media" Link Relation

   This specification adds the value "edit-media" to the Atom Registry
   of Link Relations (see Section 7.1 of [RFC4287]).  When appearing
   within an atom:entry, the value of the href attribute is an IRI that
   can be used to modify a Media Resource associated with that Entry.

   An atom:entry element MAY contain zero or more "edit-media" link
   relations.  An atom:entry MUST NOT contain more than one atom:link
   element with a "rel" attribute value of "edit-media" that has the
   same "type" and "hreflang" attribute values.  All "edit-media" link
   relations in the same Entry reference the same Resource.  If a client
   encounters multiple "edit-media" link relations in an Entry then it
   SHOULD choose a link based on the client preferences for "type" and
   "hreflang".  If a client encounters multiple "edit-media" link
   relations in an Entry and has no preference based on the "type" and
   "hreflang" attributes then the client SHOULD pick the first "edit-
   media" link relation in document order.

12.  The Atom Format Type Parameter

   The Atom Syndication Format [RFC4287] defines the "application/
   atom+xml" media type to identify both Atom Feed and Atom Entry
   Documents.  Implementation experience has demonstrated that Atom Feed
   and Entry Documents can have different processing models and that
   there are situations where they need to be differentiated.  This
   specification defines a "type" parameter used to differentiate the
   two types of Atom documents.

12.1.  The "type" parameter

   This specification defines a new "type" parameter for use with the
   "application/atom+xml" media type.  The "type" parameter has a value
   of "entry" or "feed".

   Neither the parameter name nor its value are case sensitive.



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   The value "entry" indicates that the media type identifies an Atom
   Entry Document.  The root element of the document MUST be atom:entry.

   The value "feed" indicates that the media type identifies an Atom
   Feed Document.  The root element of the document MUST be atom:feed.

   If not specified, the type is assumed to be unspecified, requiring
   Atom processors to examine the root element to determine the type of
   Atom document.

12.1.1.  Conformance

   New specifications MAY require that the "type" parameter be used to
   identify the Atom Document type.  Producers of Atom Entry Documents
   SHOULD use the "type" parameter regardless of whether or not it is
   mandatory.  Producers of Atom Feed Documents MAY use the parameter.

   Atom processors that do not recognize the "type" parameter MUST
   ignore its value and examine the root element to determine the
   document type.

   Atom processors that do recognize the "type" parameter SHOULD detect
   and report inconsistencies between the parameter's value and the
   actual type of the document's root element.

13.  Atom Publishing Controls

   This specification defines an Atom Format Structured Extension, as
   defined in Section 6 of [RFC4287], for publishing control within the
   "http://www.w3.org/2007/app" namespace.

13.1.  The "app:control" Element

   namespace app = "http://www.w3.org/2007/app"

    pubControl =
       element app:control {
       atomCommonAttributes,
       pubDraft?
       & extensionElement
    }

    pubDraft =
      element app:draft { "yes" | "no" }







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   The "app:control" element MAY appear as a child of an atom:entry that
   is being created or updated via the Atom Publishing Protocol.  The
   app:control element MUST appear only once in an Entry.  The app:
   control element is considered foreign markup as defined in Section 6
   of [RFC4287].

   The app:control element and its child elements MAY be included in
   Atom Feed or Entry Documents.

   The app:control element can contain an "app:draft" element as defined
   below, and it can contain extension elements as defined in Section 6
   of [RFC4287].

13.1.1.  The "app:draft" Element

   The inclusion of the "app:draft" element represents a request by the
   client to control the visibility of a Member Resource.  The app:draft
   element MAY be ignored by the server.

   The number of app:draft elements in app:control MUST be zero or one.
   The content of an app:draft element MUST be one of "yes" or "no".  If
   the element contains "no", this indicates a client request that the
   Member Resource be made publicly visible.  If the app:draft element
   is not present, then servers that support the extension MUST behave
   as though an app:draft element containing "no" was sent.

14.  Securing the Atom Publishing Protocol

   The Atom Publishing Protocol is based on HTTP.  Authentication
   requirements for HTTP are covered in Section 11 of [RFC2616].

   The use of authentication mechanisms to prevent POSTing or editing by
   unknown or unauthorized clients is RECOMMENDED but not required.
   When authentication is not used, clients and servers are vulnerable
   to trivial spoofing, denial-of-service, and defacement attacks.
   However, in some contexts, this is an acceptable risk.

   The type of authentication deployed is a local decision made by the
   server operator.  Clients are likely to face authentication schemes
   that vary across server deployments.  At a minimum, client and server
   implementations MUST be capable of being configured to use HTTP Basic
   Authentication [RFC2617] in conjunction with a connection made with
   TLS 1.0 [RFC2246] or a subsequent standards-track version of TLS
   (such as [RFC4346]), supporting the conventions for using HTTP over
   TLS described in [RFC2818].






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   The choice of authentication mechanism will impact interoperability.
   The minimum level of security referenced above (Basic Authentication
   with TLS) is considered good practice for Internet applications at
   the time of publication of this specification and sufficient for
   establishing a baseline for interoperability.  Implementers are
   encouraged to investigate and use alternative mechanisms regarded as
   equivalently good or better at the time of deployment.  It is
   RECOMMENDED that clients be implemented in such a way that new
   authentication schemes can be deployed.

   Because this protocol uses HTTP response status codes as the primary
   means of reporting the result of a request, servers are advised to
   respond to unauthorized or unauthenticated requests using an
   appropriate 4xx HTTP response code (e.g., 401 "Unauthorized" or 403
   "Forbidden") in accordance with [RFC2617].

15.  Security Considerations

   The Atom Publishing Protocol is based on HTTP and thus subject to the
   security considerations found in Section 15 of [RFC2616].

   The threats listed in this section apply to many protocols that run
   under HTTP.  The Atompub Working Group decided that the protection
   afforded by running authenticated HTTP under TLS (as described in
   Section 14) was sufficient to mitigate many of the problems presented
   by the attacks listed in this section.

15.1.  Denial of Service

   Atom Publishing Protocol server implementations need to take adequate
   precautions to ensure malicious clients cannot consume excessive
   server resources (CPU, memory, disk, etc.).

15.2.  Replay Attacks

   Atom Publishing Protocol server implementations are susceptible to
   replay attacks.  Specifically, this specification does not define a
   means of detecting duplicate requests.  Accidentally sent duplicate
   requests are indistinguishable from intentional and malicious replay
   attacks.

15.3.  Spoofing Attacks

   Atom Publishing Protocol implementations are susceptible to a variety
   of spoofing attacks.  Malicious clients might send Atom Entries
   containing inaccurate information anywhere in the document.





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15.4.  Linked Resources

   Atom Feed and Entry Documents can contain XML External Entities as
   defined in Section 4.2.2 of [REC-xml].  Atom implementations are not
   required to load external entities.  External entities are subject to
   the same security concerns as any network operation and can alter the
   semantics of an Atom document.  The same issues exist for Resources
   linked to by Atom elements such as atom:link and atom:content.

15.5.  Digital Signatures and Encryption

   Atom Entry and Feed Documents can contain XML Digital Signatures
   [REC-xmldsig-core] and can be encrypted using XML Encryption
   [REC-xmlenc-core] as specified in Section 5 of [RFC4287].  Handling
   of signatures and encrypted elements in Atom documents is discussed
   in Sections 5 and 6.3 of [RFC4287].

   Neither servers nor clients are under any obligation to support
   encryption and digital signature of Entries or Feeds, although it is
   certainly possible that in some installations, clients or servers
   might require signing or encrypting of the documents exchanged in the
   Atom Protocol.

   Because servers are allowed (and in some cases, expected) to modify
   the contents of an Entry Document before publishing it, signatures
   within an entry are only likely to be useful to the server to which
   the entry is being sent.  Clients cannot assume that the signature
   will be valid when viewed by a third party, or even that the server
   will publish the client's signature.

   A server is allowed to strip client-applied signatures, to strip
   client-applied signatures and then re-sign with its own public key,
   and to oversign an entry with its own public key.  The meaning to a
   third party of a signature applied by a server is the same as a
   signature from anyone, as described in [RFC4287].  It is RECOMMENDED
   that a server that is aware that it has changed any part of an Entry
   Document that was signed by the client should strip that signature
   before publishing the entry in order to prevent third parties from
   trying to interpret a signature that cannot be validated.

15.6.  URIs and IRIs

   Atom Publishing Protocol implementations handle URIs and IRIs.  See
   Section 7 of [RFC3986] and Section 8 of [RFC3987] for security
   considerations related to their handling and use.






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   The Atom Publishing Protocol leaves the server in control of minting
   URIs.  The use of any client-supplied data for creating new URIs is
   subject to the same concerns as described in the next section.

15.7.  Code Injection and Cross Site Scripting

   Atom Feed and Entry Documents can contain a broad range of content
   types including code that might be executable in some contexts.
   Malicious clients could attempt to attack servers or other clients by
   injecting code into a Collection Document's Entry or Media Resources.

   Server implementations are strongly encouraged to verify that client-
   supplied content is safe prior to accepting, processing, or
   publishing it.  In the case of HTML, experience indicates that
   verification based on a white list of acceptable content is more
   effective than a black list of forbidden content.

   Additional information about XHTML and HTML content safety can be
   found in Section 8.1 of [RFC4287].

16.  IANA Considerations

   This specification uses two new media types that conform to the
   registry mechanism described in [RFC4288], a new message header that
   conforms to the registry mechanism described in [RFC3864], and two
   new link relations that conform to the registry mechanism described
   in [RFC4287].

16.1.  Content-Type Registration for 'application/atomcat+xml'

   An Atom Publishing Protocol Category Document, when serialized as XML
   1.0, can be identified with the following media type:

   MIME media type name:  application

   MIME subtype name:  atomcat+xml

   Required parameters:  None.

   Optional parameters:

      "charset":  This parameter has identical semantics to the charset
         parameter of the "application/xml" media type as specified in
         [RFC3023].

   Encoding considerations:  Identical to those of "application/xml" as
      described in [RFC3023], Section 3.2.




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   Security considerations:  As defined in RFC 5023.

      In addition, as this media type uses the "+xml" convention, it
      shares the same security considerations as described in [RFC3023],
      Section 10.

   Interoperability considerations:  There are no known interoperability
      issues.

   Published specification:  RFC 5023.

   Applications that use this media type:  No known applications
      currently use this media type.

   Additional information:

   Magic number(s):  As specified for "application/xml" in [RFC3023],
      Section 3.2.

   File extension:  .atomcat

   Fragment identifiers:  As specified for "application/xml" in
      [RFC3023], Section 5.

   Base URI:  As specified in [RFC3023], Section 6.

   Macintosh file type code:  TEXT

   Person & email address to contact for further information:
      Joe Gregorio <joe@bitworking.org>

   Intended usage:  COMMON

   Author/Change controller:  IETF (iesg@ietf.org) Internet Engineering
      Task Force

16.2.  Content-Type Registration for 'application/atomsvc+xml'

   An Atom Publishing Protocol Service Document, when serialized as XML
   1.0, can be identified with the following media type:

   MIME media type name:  application

   MIME subtype name:  atomsvc+xml

   Required parameters:  None.





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   Optional parameters:

      "charset":  This parameter has identical semantics to the charset
         parameter of the "application/xml" media type as specified in
         [RFC3023].

   Encoding considerations:  Identical to those of "application/xml" as
      described in [RFC3023], Section 3.2.

   Security considerations:  As defined in RFC 5023.

      In addition, as this media type uses the "+xml" convention, it
      shares the same security considerations as described in [RFC3023],
      Section 10.

   Interoperability considerations:  There are no known interoperability
      issues.

   Published specification:  RFC 5023.

   Applications that use this media type:  No known applications
      currently use this media type.

   Additional information:

   Magic number(s):  As specified for "application/xml" in [RFC3023],
      Section 3.2.

   File extension:  .atomsvc

   Fragment identifiers:  As specified for "application/xml" in
      [RFC3023], Section 5.

   Base URI:  As specified in [RFC3023], Section 6.

   Macintosh file type code:  TEXT

   Person and email address to contact for further information:  Joe
      Gregorio <joe@bitworking.org>

   Intended usage:  COMMON

   Author/Change controller:  IETF (iesg@ietf.org) Internet Engineering
      Task Force







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16.3.  Header Field Registration for 'SLUG'

   Header field name:  SLUG

   Applicable protocol:  http [RFC2616]

   Status:  standard.

   Author/Change controller:  IETF (iesg@ietf.org) Internet Engineering
      Task Force

   Specification document(s):  RFC 5023.

   Related information:  None.

16.4.  The Link Relation Registration "edit"

   Attribute Value:  edit

   Description:  An IRI of an editable Member Entry.  When appearing
      within an atom:entry, the href IRI can be used to retrieve,
      update, and delete the Resource represented by that Entry.

   Expected display characteristics:  Undefined; this relation can be
      used for background processing or to provide extended
      functionality without displaying its value.

   Security considerations:  Automated agents should take care when this
      relation crosses administrative domains (e.g., the URI has a
      different authority than the current document).

16.5.  The Link Relation Registration "edit-media"

   Attribute Value:  edit-media

   Description:  An IRI of an editable Media Resource.  When appearing
      within an atom:entry, the href IRI can be used to retrieve,
      update, and delete the Media Resource associated with that Entry.

   Expected display characteristics:  Undefined; this relation can be
      used for background processing or to provide extended
      functionality without displaying its value.

   Security considerations:  Automated agents should take care when this
      relation crosses administrative domains (e.g., the URI has a
      different authority than the current document).





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16.6.  The Atom Format Media Type Parameter

   IANA has added a reference to this specification in the
   'application/atom+xml' media type registration.

17.  References

17.1.  Normative References

   [REC-xml]  Yergeau, F., Paoli, J., Bray, T., Sperberg-McQueen, C.,
              and E. Maler, "Extensible Markup Language (XML) 1.0
              (Fourth Edition)", World Wide Web Consortium
              Recommendation REC-xml-20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [REC-xml-infoset]
              Cowan, J. and R. Tobin, "XML Information Set (Second
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-infoset-20040204, February 2004,
              <http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.

   [REC-xml-names]
              Hollander, D., Bray, T., Tobin, R., and A. Layman,
              "Namespaces in XML 1.0 (Second Edition)", World Wide Web
              Consortium Recommendation REC-xml-names-20060816, August
              2006, <http://www.w3.org/TR/2006/REC-xml-names-20060816>.

   [REC-xmlbase]
              Marsh, J., "XML Base", W3C REC W3C.REC-xmlbase-20010627,
              June 2001,
              <http://www.w3.org/TR/2001/REC-xmlbase-20010627>.

   [REC-xmldsig-core]
              Solo, D., Reagle, J., and D. Eastlake, "XML-Signature
              Syntax and Processing", World Wide Web Consortium
              Recommendation REC-xmldsig-core-20020212, February 2002,
              <http://www.w3.org/TR/2002/REC-xmldsig-core-20020212>.

   [REC-xmlenc-core]
              Eastlake, D. and J. Reagle, "XML Encryption Syntax and
              Processing", World Wide Web Consortium Recommendation REC-
              xmlenc-core-20021210, December 2002,
              <http://www.w3.org/TR/2002/REC-xmlenc-core-20021210>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.





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   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4287]  Nottingham, M. and R. Sayre, "The Atom Syndication
              Format", RFC 4287, December 2005.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

17.2.  Informative References

   [NOTE-detect-lost-update]
              Nielsen, H. and D. LaLiberte, "Editing the Web: Detecting
              the Lost Update Problem Using Unreserved Checkout", World
              Wide Web Consortium NOTE NOTE-detect-lost-update, May
              1999, <http://www.w3.org/1999/04/Editing/>.




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   [REC-webarch]
              Walsh, N. and I. Jacobs, "Architecture of the World Wide
              Web, Volume One", W3C REC REC-webarch-20041215, December
              2004, <http://www.w3.org/TR/2004/REC-webarch-20041215>.

   [RNC]      Clark, J., "RELAX NG Compact Syntax", December 2001,
              <http://www.oasis-open.org/committees/relax-ng/
              compact-20021121.html>.











































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Appendix A.  Contributors

   The content and concepts within are a product of the Atom community
   and the Atompub Working Group.

Appendix B.  RELAX NG Compact Schema

   This appendix is informative.

   The Relax NG schema explicitly excludes elements in the Atom Protocol
   namespace that are not defined in this revision of the specification.
   Requirements for Atom Protocol processors encountering such markup
   are given in Sections 6.2 and 6.3 of [RFC4287].

   The Schema for Service Documents:

   # -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol

   namespace app = "http://www.w3.org/2007/app"
   namespace atom = "http://www.w3.org/2005/Atom"
   namespace xsd = "http://www.w3.org/2001/XMLSchema"
   namespace xhtml = "http://www.w3.org/1999/xhtml"
   namespace local = ""

   start = appService

   # common:attrs

   atomURI = text

   appCommonAttributes =
      attribute xml:base { atomURI }?,
      attribute xml:lang { atomLanguageTag  }?,
      attribute xml:space {"default"|"preserved"}?,
      undefinedAttribute*

   atomCommonAttributes = appCommonAttributes

   undefinedAttribute = attribute * - (xml:base | xml:space  | xml:lang
     | local:*) { text }

   atomLanguageTag = xsd:string {
      pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
   }







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   atomDateConstruct =
       appCommonAttributes,
       xsd:dateTime

   # app:service
   appService =
      element app:service {
         appCommonAttributes,
         ( appWorkspace+
           & extensionElement* )
      }

   # app:workspace

   appWorkspace =
      element app:workspace {
         appCommonAttributes,
         ( atomTitle
           & appCollection*
           & extensionSansTitleElement* )
      }

   atomTitle = element atom:title { atomTextConstruct }

   # app:collection

   appCollection =
      element app:collection {
         appCommonAttributes,
         attribute href { atomURI  },
         ( atomTitle
           & appAccept*
           & appCategories*
           & extensionSansTitleElement* )
      }

   # app:categories

   atomCategory =
       element atom:category {
          atomCommonAttributes,
          attribute term { text },
          attribute scheme { atomURI }?,
          attribute label { text }?,
          undefinedContent
       }





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   appInlineCategories =
       element app:categories {
           attribute fixed { "yes" | "no" }?,
           attribute scheme { atomURI }?,
           (atomCategory*,
           undefinedContent)
       }

   appOutOfLineCategories =
       element app:categories {
           attribute href { atomURI },
           undefinedContent
       }

   appCategories = appInlineCategories | appOutOfLineCategories

   # app:accept

   appAccept =
      element app:accept {
            appCommonAttributes,
            ( text? )
      }

   # Simple Extension

   simpleSansTitleExtensionElement =
      element * - (app:*|atom:title) {
         text
      }

   simpleExtensionElement =
      element * - (app:*) {
         text
      }

   # Structured Extension

   structuredSansTitleExtensionElement =
      element * - (app:*|atom:title) {
         (attribute * { text }+,
            (text|anyElement)*)
       | (attribute * { text }*,
          (text?, anyElement+, (text|anyElement)*))
      }






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   structuredExtensionElement =
      element * - (app:*) {
         (attribute * { text }+,
            (text|anyElement)*)
       | (attribute * { text }*,
          (text?, anyElement+, (text|anyElement)*))
      }

   # Other Extensibility

   extensionSansTitleElement =
    simpleSansTitleExtensionElement|structuredSansTitleExtensionElement

   extensionElement = simpleExtensionElement |
      structuredExtensionElement

   undefinedContent = (text|anyForeignElement)*

   # Extensions

   anyElement =
      element * {
         (attribute * { text }
          | text
          | anyElement)*
      }

   anyForeignElement =
       element * - app:* {
          (attribute * { text }
           | text
           | anyElement)*
       }

   atomPlainTextConstruct =
       atomCommonAttributes,
       attribute type { "text" | "html" }?,
       text

   atomXHTMLTextConstruct =
       atomCommonAttributes,
       attribute type { "xhtml" },
       xhtmlDiv

   atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct






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   anyXHTML = element xhtml:* {
       (attribute * { text }
        | text
        | anyXHTML)*
   }

   xhtmlDiv = element xhtml:div {
     (attribute * { text }
      | text
      | anyXHTML)*
   }

   # EOF

   The Schema for Category Documents:

   # -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol

   namespace app = "http://www.w3.org/2007/app"
   namespace atom = "http://www.w3.org/2005/Atom"
   namespace xsd = "http://www.w3.org/2001/XMLSchema"
   namespace local = ""

   start = appCategories

   atomCommonAttributes =
      attribute xml:base { atomURI }?,
      attribute xml:lang { atomLanguageTag }?,
      undefinedAttribute*

   undefinedAttribute = attribute * - (xml:base | xml:lang | local:*) {
     text }

   atomURI = text

   atomLanguageTag = xsd:string {
      pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
   }

   atomCategory =
       element atom:category {
          atomCommonAttributes,
          attribute term { text },
          attribute scheme { atomURI }?,
          attribute label { text }?,
          undefinedContent
       }




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   appInlineCategories =
       element app:categories {
           attribute fixed { "yes" | "no" }?,
           attribute scheme { atomURI }?,
           (atomCategory*,
           undefinedContent)
       }

   appOutOfLineCategories =
       element app:categories {
           attribute href { atomURI },
           (empty)
       }

   appCategories = appInlineCategories | appOutOfLineCategories

   # Extensibility

   undefinedContent = (text|anyForeignElement)*

   anyElement =
      element * {
         (attribute * { text }
          | text
          | anyElement)*
      }

   anyForeignElement =
       element * - atom:* {
          (attribute * { text }
           | text
           | anyElement)*
       }

   # EOF
















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Authors' Addresses

   Joe Gregorio (editor)
   Google

   EMail: joe@bitworking.org
   URI:   http://bitworking.org/


   Bill de hOra (editor)
   NewBay Software

   EMail: bill@dehora.net
   URI:   http://dehora.net/





































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
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   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
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   attempt made to obtain a general license or permission for the use of
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   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
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   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.












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