Atom配信フォーマット（共通のAtomコンストラクト）

   Many of Atom's elements share a few common structures.  This section
   defines those structures and their requirements for convenient
   reference by the appropriate element definitions.

   When an element is identified as being a particular kind of
   construct, it inherits the corresponding requirements from that
   construct's definition in this section.

   Note that there MUST NOT be any white space in a Date construct or in
   any IRI.  Some XML-emitting implementations erroneously insert white
   space around values by default, and such implementations will emit
   invalid Atom Documents.

   A Text construct contains human-readable text, usually in small
   quantities.  The content of Text constructs is Language-Sensitive.

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

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

   atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct

   Text constructs MAY have a "type" attribute.  When present, the value
   MUST be one of "text", "html", or "xhtml".  If the "type" attribute
   is not provided, Atom Processors MUST behave as though it were
   present with a value of "text".  Unlike the atom:content element
   defined in Section 4.1.3, MIME media types [MIMEREG] MUST NOT be used
   as values for the "type" attribute on Text constructs.

   Example atom:title with text content:

   ...
   <title type="text">
     Less: <
   </title>
   ...

   If the value is "text", the content of the Text construct MUST NOT
   contain child elements.  Such text is intended to be presented to
   humans in a readable fashion.  Thus, Atom Processors MAY collapse
   white space (including line breaks) and display the text using
   typographic techniques such as justification and proportional fonts.

   Example atom:title with HTML content:

   ...
   <title type="html">
     Less: &lt;em&gt; &amp;lt; &lt;/em&gt;
   </title>
   ...

   If the value of "type" is "html", the content of the Text construct
   MUST NOT contain child elements and SHOULD be suitable for handling
   as HTML [HTML].  Any markup within MUST be escaped; for example,
   "<br>" as "&lt;br&gt;".  HTML markup within SHOULD be such that it could
   validly appear directly within an HTML <DIV> element, after
   unescaping.  Atom Processors that display such content MAY use that
   markup to aid in its display.

   Example atom:title with XHTML content:

   ...
   <title type="xhtml" xmlns:xhtml="http://www.w3.org/1999/xhtml">
     <xhtml:div>
       Less: <xhtml:em> &lt; </xhtml:em>
     </xhtml:div>
   </title>
   ...

   If the value of "type" is "xhtml", the content of the Text construct
   MUST be a single XHTML div element [XHTML] and SHOULD be suitable for
   handling as XHTML.  The XHTML div element itself MUST NOT be
   considered part of the content.  Atom Processors that display the
   content MAY use the markup to aid in displaying it.  The escaped
   versions of characters such as "&" and ">" represent those
   characters, not markup.

   Examples of valid XHTML content:

   ...
   <summary type="xhtml">
      <div xmlns="http://www.w3.org/1999/xhtml">
         This is <b>XHTML</b> content.
      </div>
   </summary>
   ...
   <summary type="xhtml">
      <xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
         This is <xhtml:b>XHTML</xhtml:b> content.
      </xhtml:div>
   </summary>
   ...

   The following example assumes that the XHTML namespace has been bound
   to the "xh" prefix earlier in the document:

   ...
   <summary type="xhtml">
      <xh:div>
         This is <xh:b>XHTML</xh:b> content.
      </xh:div>
   </summary>
   ...

   A Person construct is an element that describes a person,
   corporation, or similar entity (hereafter, 'person').

   atomPersonConstruct =
      atomCommonAttributes,
      (element atom:name { text }
       & element atom:uri { atomUri }?
       & element atom:email { atomEmailAddress }?
       & extensionElement*)

   This specification assigns no significance to the order of appearance
   of the child elements in a Person construct.  Person constructs allow
   extension Metadata elements (see Section 6.4).

   The "atom:name" element's content conveys a human-readable name for
   the person.  The content of atom:name is Language-Sensitive.  Person
   constructs MUST contain exactly one "atom:name" element.

   The "atom:uri" element's content conveys an IRI associated with the
   person.  Person constructs MAY contain an atom:uri element, but MUST
   NOT contain more than one.  The content of atom:uri in a Person
   construct MUST be an IRI reference [RFC3987].

   The "atom:email" element's content conveys an e-mail address
   associated with the person.  Person constructs MAY contain an
   atom:email element, but MUST NOT contain more than one.  Its content
   MUST conform to the "addr-spec" production in [RFC2822].

   A Date construct is an element whose content MUST conform to the
   "date-time" production in [RFC3339].  In addition, an uppercase "T"
   character MUST be used to separate date and time, and an uppercase
   "Z" character MUST be present in the absence of a numeric time zone
   offset.

   atomDateConstruct =
      atomCommonAttributes,
      xsd:dateTime

   Such date values happen to be compatible with the following
   specifications: [ISO.8601.1988], [W3C.NOTE-datetime-19980827], and
   [W3C.REC-xmlschema-2-20041028].

   Example Date constructs:

   <updated>2003-12-13T18:30:02Z</updated>
   <updated>2003-12-13T18:30:02.25Z</updated>
   <updated>2003-12-13T18:30:02+01:00</updated>
   <updated>2003-12-13T18:30:02.25+01:00</updated>

   Date values SHOULD be as accurate as possible.  For example, it would
   be generally inappropriate for a publishing system to apply the same
   timestamp to several entries that were published during the course of
   a single day.