repo_zf1/documentation/manual/de/module_specs/Zend_Feed_Reader.xml

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<sect1 id="zend.feed.reader">
    <title>Zend_Feed_Reader</title>

    <sect2 id="zend.feed.reader.introduction">
        <title>Einführung</title>

        <para>
            <classname>Zend_Feed_Reader</classname> ist eine Komponente die verwendet wird um
            <acronym>RSS</acronym> und Atom Feeds jeder Version zu konsumieren, inklusive
            <acronym>RDF</acronym>/<acronym>RSS</acronym> 1.0, <acronym>RSS</acronym> 2.0 und
            Atom 0.3/1.0. Die <acronym>API</acronym> für das Empfangen von Feed Daten ist relativ
            einfach da <classname>Zend_Feed_Reader</classname> in der Lage ist jeden Feed eines
            jeden Typs mit Hilfe der <acronym>API</acronym> nach den angefragten Informationen zu
            durchsuchen. Wenn die typischen Elemente die diese Informationen enthalten nicht
            vorhanden sind, werden diese adaptiert und statt dessen auf eine Vielzahl von
            alternativen Elementen zurück gegriffen. Diese Fähigkeit, von Alternativen auszuwählen,
            verhindert das Benutzer Ihren eigenen astrakten Layer über die Komponente legen müssen
            damit Sie nützlich ist, oder beliebig tiefes Wissen des zugrundeliegenden Standard,
            aktueller alternativen und namespaces Erweiterungen haben müssen.
        </para>

        <para>
            Intern arbeitet <classname>Zend_Feed_Reader</classname> fast komplett auf Basis der
            Erstellung von XPath Abfragen gegen das Dokument Objekt Modell des Feed
            <acronym>XML</acronym>'s. Das <acronym>DOM</acronym> wird nicht durch eine gekettete
            Eigenschaften <acronym>API</acronym> wie bei <classname>Zend_Feed</classname> bekannt
            gegeben und durch die darunterliegenden <classname>DOMDocument</classname>,
            <classname>DOMElement</classname> und <classname>DOMXPath</classname> Objekte für eine
            externe Manipulation bekannt gegeben. Dieser Singular Weg des Parsens ist Konsistent
            und die Komponente bietet ein Plugin System um dem Feed hinzuzufügen und eine Eintrags
            Level <acronym>API</acronym> durch das Schreiben von Erweiterungen auf einer ähnlichen
            Basis.
        </para>

        <para>
            Geschwindigkeit wird auf drei Wegen bereitgestellt. Erstens unterstützt
            <classname>Zend_Feed_Reader</classname> das Cachen durch Verwendung von
            <classname>Zend_Cache</classname> um eine Kopie des Originalen Feed
            <acronym>XML</acronym> zu halten. Das erlaubt es Netzwerk Anfragen für eine Feed
            <acronym>URI</acronym> zu überspringen wenn der Cache gültig ist. Zweitens wird die
            Feed und Eintrag- Level <acronym>API</acronym> durch einen internen Cache gesichert
            (nicht persistent) damit wiederholte <acronym>API</acronym> Aufrufe für den gleichen
            Feed eine zusätzliche Verwendung von <acronym>DOM</acronym>/XPath verhindert.
            Drittens erlaubt das Importieren von Feeds von einer <acronym>URI</acronym> den
            Vorteil von konditionellen <acronym>HTTP</acronym> GET Anfragen was es Servern
            erlaubt eine leere 304 Anfrage auszulösen wenn der angefragte Fed seit der Zeit zu der
            er das letzte Mal angefragt wurde, nicht verändert wurde. Im letzten Fall hält eine
            Instanz von <classname>Zend_Cache</classname> den zuletzt empfangenen Feed zusammen mit
            dem ETag und dem Last-Modified Header Werten die in der <acronym>HTTP</acronym>
            Antwort gesendet wurde.
        </para>

        <para>
            Relativ zu <classname>Zend_Feed</classname> wurde
            <classname>Zend_Feed_Reader</classname> als frei stehender Ersatz für
            <classname>Zend_Feed</classname> formuliert der aber nicht mit
            <classname>Zend_Feed</classname> rückwärts kompatibel ist. Aber es ist eine Alternative
            die einer anderen Ideologie folgt die darin fokusiert ist einfach verwendbar zu sein,
            flexibel, konsistent und durch das Plugin System erweiterbar.
            <classname>Zend_Feed_Reader</classname> ist auch nicht dazu fähig Feeds zu erstellen,
            das wird aber zu einem späteren Zeitpunkt hinzugefügt.
        </para>
    </sect2>

    <sect2 id="zend.feed.reader.import">
        <title>Feeds importieren</title>

        <para>
            Das importieren eines Feeds mit <classname>Zend_Feed_Reader</classname> ist zu
            <classname>Zend_Feed</classname> nicht sehr unterschiedlich. Feeds können von einem
            String, einer Datei, <acronym>URI</acronym> oder einer Instanz des Typs
            <classname>Zend_Feed_Abstract</classname> importiert werden. Das importieren von einer
            <acronym>URI</acronym> kann zusätzlich eine konditionelle <acronym>HTTP</acronym>
            GET Anfrage benützen. Wenn das importieren fehlschlägt, wird eine Exception geworfen.
            Das Endergebnis wird ein Objekt des Typs
            <classname>Zend_Feed_Reader_FeedInterface</classname> sein, die Core Implementation
            von <classname>Zend_Feed_Reader_Feed_Rss</classname> und
            <classname>Zend_Feed_Reader_Feed_Atom</classname> (<classname>Zend_Feed</classname>
            hat alle kurzen Namen genommen!). Beide Objekte unterstützen mehrere (alle
            existierenden) Versionen dieser breiten Feed Typen.
        </para>

        <para>
            Im folgenden Beispiel importieren wir einen
            <acronym>RDF</acronym>/<acronym>RSS</acronym> 1.0 Feed und extrahieren einige
            grundsätzliche Information die dann in einer Datenbank oder wo anders gespeichert
            werden können.
        </para>

        <programlisting language="php"><![CDATA[
$feed = Zend_Feed_Reader::import('http://www.planet-php.net/rdf/');
$data = array(
    'title'        => $feed->getTitle(),
    'link'         => $feed->getLink(),
    'dateModified' => $feed->getDateModified(),
    'description'  => $feed->getDescription(),
    'language'     => $feed->getLanguage(),
    'entries'      => array(),
);

foreach ($feed as $entry) {
    $edata = array(
        'title'        => $entry->getTitle(),
        'description'  => $entry->getDescription(),
        'dateModified' => $entry->getDateModified(),
        'author'       => $entry->getAuthor(),
        'link'         => $entry->getLink(),
        'content'      => $entry->getContent()
    );
    $data['entries'][] = $edata;
}
]]></programlisting>

        <para>
            Das obige Beispiel demonstriert die <acronym>API</acronym> von
            <classname>Zend_Feed_Reader</classname> und es demonstriert auch einige seiner
            internen Operationen. In Wirklichkeit hat der ausgewählte <acronym>RDF</acronym> Feed
            keine nativen Daten oder Author Elemente, trotzdem verwendet er das Dublin Core 1.1
            Modul welches Namespaced Ersteller und Datums Elemente anbietet.
            <classname>Zend_Feed_Reader</classname> fällt auf diese und ähnliche Operationen zurück
            wenn keine relativ nativen Elemente existieren. Wenn es absolut keine alternative
            finden kann wird es <constant>NULL</constant> zurückgeben, was anzeigt das die
            Informationen nicht im Feed gefunden werden können. Man sollte beachten das Klassen die
            <classname>Zend_Feed_Reader_FeedInterface</classname> implementieren auch
            die <acronym>SPL</acronym> Interfaces <classname>Iterator</classname> und
            <classname>Countable</classname> implementieren.
        </para>

        <para>
            Feeds können auch von Strings, Dateien und sogar Objekten des Typs
            <classname>Zend_Feed_Abstract</classname> importiert werden.
        </para>

        <programlisting language="php"><![CDATA[
// von einer URI
$feed = Zend_Feed_Reader::import('http://www.planet-php.net/rdf/');

// von einem String
$feed = Zend_Feed_Reader::importString($feedXmlString);

// von einer Datei
$feed = Zend_Feed_Reader::importFile('./feed.xml');

// von einem abstrakten Zend_Feed_Abstract Objekt
$zfeed = Zend_Feed::import('http://www.planet-php.net/atom/');
$feed  = Zend_Feed_Reader::importFeed($zfeed);
]]></programlisting>
    </sect2>

    <sect2 id="zend.feed.reader.sources">
        <title>Empfangen darunterliegender Quellen von Feeds und Einträgen</title>

        <para>
            <classname>Zend_Feed_Reader</classname> macht sein bestes um Ihnen die Details
            abzunehmen. Wenn man an einem Feed ausserhalb von
            <classname>Zend_Feed_Reader</classname> arbeiten muß, kann man das grundsätzliche
            <classname>DOMDocument</classname> oder <classname>DOMElement</classname> von jeder
            Klasse extrahieren, oder sogar einen <acronym>XML</acronym> String der sie enthält.
            Es werden auch Methoden angeboten um das aktuelle <classname>DOMXPath</classname>
            Objekt (mit allen registrierten Kern und Erweiterungs Namespaces) zu extrahieren, und
            den richtigen Präfix der in allen XPath Anfragen für den aktuellen Feed oder Eintrag
            verwendet wird. Die grundsätzlich zu verwenden Methoden (für jedes Objekt) sind
            <methodname>saveXml()</methodname>, <methodname>getDomDocument()</methodname>,
            <methodname>getElement()</methodname>, <methodname>getXpath()</methodname> und
            <methodname>getXpathPrefix()</methodname>. Diese erlauben es sich von
            <classname>Zend_Feed_Reader</classname> zu lösen und das zu tun was man selbst
            machen will.
        </para>

        <itemizedlist>
            <listitem>
                <para>
                    <methodname>saveXml()</methodname> gibt einen <acronym>XML</acronym> String
                    zurück der nur das Element enthält welches das aktuelle Objekt repräsentiert.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getDomDocument()</methodname> gibt das
                    <classname>DOMDocument</classname> Objekt zurück das den kompletten Feed
                    repräsentiert (sogar wenn es von einem Entry Objekt aus aufgerufen wird).
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getElement()</methodname> gibt das <classname>DOMElement</classname>
                    des aktuellen Objekts zurück (z.B. den Feed oder aktuellen Eintrag).
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getXpath()</methodname> gibt das aktuelle
                    <classname>DOMXPath</classname> Objekt für den aktuellen Feed zurück (sogar wenn
                    es von einem Entry Objekt aus aufgerufen wird) mit den Namespaces des aktuellen
                    Feed Typs und allen vor-registrierten geladenen Erweiterungen.
                </para>
            </listitem>

            <listitem>
                <para>
                    <methodname>getXpathPrefix()</methodname> gibt den Präfix der Abfrage für das
                    aktuelle Objekt zurück (z.B. den Feed oder den aktuellen Eintrag) welcher den
                    richtigen XPath Query Pfad für den spezifizierten Feed oder Eintrag enthält.
                </para>
            </listitem>
        </itemizedlist>

        <para>
            Hier ist ein Beispiel bei dem ein Feed eine <acronym>RSS</acronym> Erweiterung enthalten
            können die von <classname>Zend_Feed_Reader</classname> nicht out of the Box unterstützt
            wird. Beachtenswert ist, das man eine Erweiterungen schreiben und registrieren könnte
            (wird später behandelt) um das zu bewerkstelligen, aber das ist nicht immer eine
            Garantie für einen schnellen Check. Man muß jeden neuen Namespace beim
            <classname>DOMXPath</classname> Objekt registrieren bevor es verwendet wird ausser Sie
            werden vorab von <classname>Zend_Feed_Reader</classname> oder einer Erweiterung
            registriert.
        </para>

        <programlisting language="php"><![CDATA[
$feed        = Zend_Feed_Reader::import('http://www.planet-php.net/rdf/');
$xpathPrefix = $feed->getXpathPrefix();
$xpath       = $feed->getXpath();
$xpath->registerNamespace('admin', 'http://webns.net/mvcb/');
$reportErrorsTo = $xpath->evaluate('string('
                                 . $xpathPrefix
                                 . '/admin:errorReportsTo)');
]]></programlisting>

        <warning>
            <para>
                Wenn man einen bereits registrierten Namespace mit einem anderen Präfix Namen
                registriert als jenen der von <classname>Zend_Feed_Reader</classname> intern
                verwendet wird, zerstört das die Interne Arbeitsweise dieser Komponente.
            </para>
        </warning>
    </sect2>

    <sect2 id="zend.feed.reader.cache-request">
        <title>Unterstützung für Caches und intelligente Anfragen</title>

        <sect3 id="zend.feed.reader.cache-request.cache">
            <title>Unterstützung für Caches in Zend_Feed_Reader hinzufügen</title>

            <para>
                <classname>Zend_Feed_Reader</classname> unterstützt die Verwendung einer Instanz von
                <classname>Zend_Cache</classname> um Feeds zu cachen (als <acronym>XML</acronym>)
                um unnötige Anfragen im Netzwerk zu vermeiden. Das Hinzufügen eines Caches ist hier
                so einfach wie bei anderen Zend Framework Komponenten. Den Cache erstellen und
                konfigurieren und dann <classname>Zend_Feed_Reader</classname> mitteilen das er
                verwendet werden soll! Der verwendete Cache Schlüssel ist
                "<classname>Zend_Feed_Reader_</classname>" gefolgt von dem
                <acronym>MD5</acronym> Hash der <acronym>URI</acronym> des Feeds.
            </para>

            <programlisting language="php"><![CDATA[
$frontendOptions = array(
   'lifetime' => 7200,
   'automatic_serialization' => true
);
$backendOptions = array('cache_dir' => './tmp/');
$cache = Zend_Cache::factory(
    'Core', 'File', $frontendOptions, $backendOptions
);

Zend_Feed_Reader::setCache($cache);
]]></programlisting>

            <note>
                <para>
                    Auch wenn es etwas abseits ist, sollte man daran denken zu
                    <classname>Zend_Loader_PluginLoader</classname> einen Cache hinzuzufügen der
                    von <classname>Zend_Feed_Reader</classname> verwendet wird um Erweiterungen zu
                    laden.
                </para>
            </note>
        </sect3>

        <sect3 id="zend.feed.reader.cache-request.http-conditional-get">
            <title>Unterstützung für HTTP Conditional GET</title>

            <para>
                Die große Frage wenn man ofters einen Feed importiert, ist ob er sich geändert hat.
                Wenn ein Cache aktiviert ist, kann man die Unterstützung für <acronym>HTTP</acronym>
                Conditional GET hinzufügen um diese Frage zu beantworten.
            </para>

            <para>
                Using this method, you can request feeds from <acronym>URI</acronym>s and include
                their last known ETag and Last-Modified response header values
                with the request (using the If-None-Match and If-Modified-Since
                headers). If the feed on the server remains unchanged, you
                should receive a 304 response which tells
                <classname>Zend_Feed_Reader</classname> to use the cached
                version. If a full feed is sent in a response with a status code
                of 200, this means the feed has changed and
                <classname>Zend_Feed_Reader</classname> will parse the new
                version and save it to the cache. It will also cache the new
                ETag and Last-Modified header values for future use.
            </para>

            <para>
                These "conditional" requests are not guaranteed to be supported
                by the server you request a <acronym>URI</acronym> of, but can be attempted
                regardless. Most common feed sources like blogs should however
                have this supported. To enable conditional requests, you will
                need to provide a cache to <classname>Zend_Feed_Reader</classname>.
            </para>

            <programlisting language="php"><![CDATA[
$frontendOptions = array(
   'lifetime' => 86400,
   'automatic_serialization' => true
);
$backendOptions = array('cache_dir' => './tmp/');
$cache = Zend_Cache::factory(
    'Core', 'File', $frontendOptions, $backendOptions
);

Zend_Feed_Reader::setCache($cache);
Zend_Feed_Reader::useHttpConditionalGet();

$feed = Zend_Feed_Reader::import('http://www.planet-php.net/rdf/');
]]></programlisting>

            <para>
                In the example above, with <acronym>HTTP</acronym> Conditional GET requests enabled,
                the response header values for ETag and Last-Modified will be cached
                along with the feed. For the next 24hrs (the cache lifetime), feeds will
                only be updated on the cache if a non-304 response is received
                containing a valid <acronym>RSS</acronym> or Atom <acronym>XML</acronym> document.
            </para>

            <para>
                If you intend on managing request headers from outside
                <classname>Zend_Feed_Reader</classname>, you can set the
                relevant If-None-Matches and If-Modified-Since request headers
                via the <acronym>URI</acronym> import method.
            </para>

            <programlisting language="php"><![CDATA[
$lastEtagReceived = '5e6cefe7df5a7e95c8b1ba1a2ccaff3d';
$lastModifiedDateReceived = 'Wed, 08 Jul 2009 13:37:22 GMT';
$feed = Zend_Feed_Reader::import(
    $uri, $lastEtagReceived, $lastModifiedDateReceived
);
]]></programlisting>
        </sect3>
    </sect2>

    <sect2 id="zend.feed.reader.locate">
        <title>Locating Feed URIs from Websites</title>

        <para>
            These days, many websites are aware that the location of their <acronym>XML</acronym>
            feeds is not always obvious. A small <acronym>RDF</acronym>, <acronym>RSS</acronym> or
            Atom graphic helps when the user is reading the page, but what about when a machine
            visits trying to identify where your feeds are located? To assist in
            this, websites may point to their feeds using &lt;link&gt; tags in
            the &lt;head&gt; section of their <acronym>HTML</acronym>. To take advantage of this,
            you can use <classname>Zend_Feed_Reader</classname> to locate these
            feeds using the static <methodname>findFeedLinks()</methodname>
            method.
        </para>

        <para>
            This method calls any <acronym>URI</acronym> and searches for the location of
            <acronym>RSS</acronym>, <acronym>RDF</acronym>
            and Atom feeds assuming the wlebsite's <acronym>HTML</acronym> contains the relevant
            links. It then returns a value object where you can check for the existence of a
            <acronym>RSS</acronym>, <acronym>RDF</acronym> or Atom feed <acronym>URI</acronym>.
        </para>

        <programlisting language="php"><![CDATA[
$links = Zend_Feed_Reader::findFeedLinks('http://www.planet-php.net');

if(isset($links->rdf)) {
    echo $links->rdf, "\n"; // http://www.planet-php.org/rdf/
}
if(isset($links->rss)) {
    echo $links->rss, "\n"; // http://www.planet-php.org/rss/
}
if(isset($links->atom)) {
    echo $links->atom, "\n"; // http://www.planet-php.org/atom/
}
]]></programlisting>

        <para>
            Based on these links, you can then import from whichever source you
            wish in the usual manner.
        </para>
  </sect2>

  <sect2 id="zend.feed.reader.retrieve-info">
        <title>Retrieving Feed Information</title>

        <para>
            Retrieving information from a feed (we'll cover entries/items in the
            next section though they follow identical principals) uses a clearly
            defined <acronym>API</acronym> which is exactly the same regardless of whether the feed
            in question is <acronym>RSS</acronym>/<acronym>RDF</acronym>/Atom. The same goes for
            sub-versions of these standards and we've tested every single
            <acronym>RSS</acronym> and Atom version. While
            the underlying feed <acronym>XML</acronym> can differ substantially in terms of the
            tags and elements they present, they nonetheless are all trying to
            convey similar information and to reflect this all the differences
            and wrangling over alternative tags are handled internally by
            <classname>Zend_Feed_Reader</classname> presenting you with an
            identical interface for each. Ideally, you should not have to care
            whether a feed is <acronym>RSS</acronym> or Atom so long as you can extract the
            information you want.
        </para>

        <para>
            Of course, we don't live in an ideal world so there may be times the
            <acronym>API</acronym> just does not cover what you're looking for. To assist you,
            <classname>Zend_Feed_Reader</classname> offers a plugin system which
            allows you to write Extensions to expand the core <acronym>API</acronym> and cover any
            additional data you are trying to extract from feeds. If writing
            another Extension is too much trouble, you can simply grab the
            underlying <acronym>DOM</acronym> or XPath objects and do it by hand in your
            application. Of course, we really do encourage writing an Extension
            simply to make it more portable and reusable.
        </para>

        <para>
            Here's a summary of the Core <acronym>API</acronym> for Feeds. You should note it
            comprises not only the basic <acronym>RSS</acronym> and Atom standards, but also
            accounts for a number of included Extensions bundled with
            <classname>Zend_Feed_Reader</classname>. The naming of these
            Extension sourced methods remain fairly generic - all Extension
            methods operate at the same level as the Core <acronym>API</acronym> though we do allow
            you to retrieve any specific Extension object separately if
            required.
        </para>

        <table>
            <title>Feed Level API Methods</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry><methodname>getId()</methodname></entry>

                        <entry>Returns a unique ID associated with this feed</entry>
                    </row>

                    <row>
                        <entry><methodname>getTitle()</methodname></entry>

                        <entry>Returns the title of the feed</entry>
                    </row>

                    <row>
                        <entry><methodname>getDescription()</methodname></entry>

                        <entry>Returns the text description of the feed</entry>
                    </row>

                    <row>
                        <entry><methodname>getLink()</methodname></entry>

                        <entry>
                            Returns a <acronym>URI</acronym> to the <acronym>HTML</acronym> website
                            containing the same or
                            similar information as this feed (i.e. if the feed is from a blog,
                            it should provide the blog's <acronym>URI</acronym> where the
                            <acronym>HTML</acronym> version of the entries can be read).
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getFeedLink()</methodname></entry>

                        <entry>
                            Returns the <acronym>URI</acronym> of this feed, which should be the
                            same as the <acronym>URI</acronym> used to import the feed
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getAuthors()</methodname></entry>

                        <entry>
                            Returns an array of all authors associated with this feed
                            including email address in the author string if available
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getAuthor(integer $index = 0)</methodname></entry>

                        <entry>
                            Returns either the first author known, or with the
                            optional <varname>$index</varname> parameter any specific
                            index on the array of Authors (returning null if an
                            invalid index).
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getDateCreated()</methodname></entry>

                        <entry>
                            Returns the date on which this feed was created. Generally
                            only applicable to Atom where it represents the date the resource
                            described by an Atom 1.0 document was created.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getDateModified()</methodname></entry>

                        <entry>
                            Returns the date on which this feed was last modified
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getLanguage()</methodname></entry>

                        <entry>
                            Returns the language of the feed (if defined) or simply the
                            language noted in the <acronym>XML</acronym> document
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getGenerator()</methodname></entry>

                        <entry>
                            Returns the generator of the feed, e.g. the software which
                            generated it. This may differ between <acronym>RSS</acronym> and Atom
                            since Atom defines a different notation.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getCopyright()</methodname></entry>

                        <entry>
                            Returns any copyright notice associated with the feed
                        </entry>
                    </row>
        </tbody>
      </tgroup>
    </table>

        <para>
            Given the variety of feeds in the wild, some of these methods will
            undoubtedly return <constant>NULL</constant> indicating the relevant information
            couldn't be located. Where possible, <classname>Zend_Feed_Reader</classname>
            will fall back on alternative elements during its search. For
            example, searching an <acronym>RSS</acronym> feed for a modification date is more
            complicated than it looks. <acronym>RSS</acronym> 2.0 feeds should include a
            <code>&lt;lastBuildDate&gt;</code> tag and/or a
            <code>&lt;pubDate&gt;</code> element. But what if it doesn't, maybe
            this is an <acronym>RSS</acronym> 1.0 feed? Perhaps it instead has an
            <code>&lt;atom:updated&gt;</code> element with identical information
            (Atom may be used to supplement <acronym>RSS</acronym>'s syntax)? Failing that, we
            could simply look at the entries, pick the most recent, and use its
            <code>&lt;pubDate&gt;</code> element. Assuming it exists... Many
            feeds also use Dublin Core 1.0/1.1 <code>&lt;dc:date&gt;</code>
            elements for feeds/entries. Or we could find Atom lurking again.
        </para>

        <para>
            The point is, <classname>Zend_Feed_Reader</classname> was designed
            to know this. When you ask for the modification date (or anything
            else), it will run off and search for all these alternatives until
            it either gives up and returns <constant>NULL</constant>, or finds an
            alternative that should have the right answer.
        </para>

        <para>
            In addition to the above methods, all Feed objects implement methods
            for retrieving the <acronym>DOM</acronym> and XPath objects for the current feeds as
            described earlier. Feed objects also implement the <acronym>SPL</acronym> Iterator and
            Countable interfaces. The extended <acronym>API</acronym> is summarised below.
        </para>

        <table>
            <title>Extended Feed Level API Methods</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry><methodname>getDomDocument()</methodname></entry>

                        <entry>
                            Returns the parent
                            <classname>DOMDocument</classname> object for the
                            entire source <acronym>XML</acronym> document
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getElement()</methodname></entry>

                        <entry>
                            Returns the current feed level
                            <classname>DOMElement</classname> object
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>saveXml()</methodname></entry>

                        <entry>
                            Returns a string containing an <acronym>XML</acronym> document of the
                            entire feed element (this is not the original
                            document but a rebuilt version)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getXpath()</methodname></entry>

                        <entry>
                            Returns the <classname>DOMXPath</classname> object
                            used internally to run queries on the
                            <classname>DOMDocument</classname> object (this
                            includes core and Extension namespaces
                            pre-registered)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getXpathPrefix()</methodname></entry>

                        <entry>
                            Returns the valid <acronym>DOM</acronym> path prefix prepended
                            to all XPath queries matching the feed being queried
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getEncoding()</methodname></entry>

                        <entry>
                            Returns the encoding of the source <acronym>XML</acronym> document
                            (note: this cannot account for errors such as the
                            server sending documents in a different encoding)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>count()</methodname></entry>

                        <entry>
                            Returns a count of the entries or items this feed contains
                            (implements <acronym>SPL</acronym> <classname>Countable</classname>
                            interface)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>current()</methodname></entry>

                        <entry>
                            Returns either the current entry (using the current index
                            from <methodname>key()</methodname>)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>key()</methodname></entry>

                        <entry>Returns the current entry index</entry>
                    </row>

                    <row>
                        <entry><methodname>next()</methodname></entry>

                        <entry>Increments the entry index value by one</entry>
                    </row>

                    <row>
                        <entry><methodname>rewind()</methodname></entry>

                        <entry>Resets the entry index to 0</entry>
                    </row>

                    <row>
                        <entry><methodname>valid()</methodname></entry>

                        <entry>
                            Checks that the current entry index is valid, i.e.
                            it does fall below 0 and does not exceed the number
                            of entries existing.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getExtensions()</methodname></entry>

                        <entry>
                            Returns an array of all Extension objects loaded for
                            the current feed (note: both feed-level and entry-level Extensions
                            exist, and only feed-level Extensions are returned here).
                            The array keys are of the form {ExtensionName}_Feed.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getExtension(string $name)</methodname></entry>

                        <entry>
                            Returns an Extension object for the feed registered under the
                            provided name. This allows more fine-grained access to
                            Extensions which may otherwise be hidden within the implementation
                            of the standard <acronym>API</acronym> methods.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getType()</methodname></entry>

                        <entry>
                            Returns a static class constant (e.g.
                            <constant>Zend_Feed_Reader::TYPE_ATOM_03</constant>,
                            i.e. Atom 0.3) indicating exactly what kind of feed
                            is being consumed.
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </table>
    </sect2>

    <sect2 id="zend.feed.reader.entry">
        <title>Retrieving Entry/Item Information</title>

        <para>
            Retrieving information for specific entries or items (depending on
            whether you speak Atom or <acronym>RSS</acronym>) is identical to feed level data.
            Accessing entries is simply a matter of iterating over a Feed object
            or using the <acronym>SPL</acronym> <classname>Iterator</classname> interface Feed
            objects implement and calling the appropriate method on each.
        </para>

        <table>
            <title>Entry Level API Methods</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry><methodname>getId()</methodname></entry>

                        <entry>Returns a unique ID for the current entry</entry>
                    </row>

                    <row>
                        <entry><methodname>getTitle()</methodname></entry>

                        <entry>Returns the title of the current entry</entry>
                    </row>

                    <row>
                        <entry><methodname>getDescription()</methodname></entry>

                        <entry>Returns a description of the current entry</entry>
                    </row>

                    <row>
                        <entry><methodname>getLink()</methodname></entry>

                        <entry>
                            Returns a <acronym>URI</acronym> to the <acronym>HTML</acronym> version
                            of the current entry
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getPermaLink()</methodname></entry>

                        <entry>
                            Returns the permanent link to the current entry
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getAuthors()</methodname></entry>

                        <entry>
                            Returns an array of all authors associated with this entry
                            including email address in the author string if available
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getAuthor($index = 0)</methodname></entry>

                        <entry>
                            Returns either the first author known, or with the
                            optional <varname>$index</varname> parameter any specific
                            index on the array of Authors (returning null if an
                            invalid index).
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getDateCreated()</methodname></entry>

                        <entry>
                            Returns the date on which the current entry was
                            created. Generally only applicable to Atom where it
                            represents the date the resource described by an
                            Atom 1.0 document was created.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getDateModified()</methodname></entry>

                        <entry>
                            Returns the date on which the current entry was last
                            modified
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getContent()</methodname></entry>

                        <entry>
                            Returns the content of the current entry (this has any
                            entities reversed if possible assuming the content type is
                            <acronym>HTML</acronym>). The description is returned if a
                            separate content element does not exist.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getCommentCount()</methodname></entry>

                        <entry>
                            Returns the number of comments made on this entry at the
                            time the feed was last generated
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getCommentLink()</methodname></entry>

                        <entry>
                            Returns a <acronym>URI</acronym> pointing to the <acronym>HTML</acronym>
                            page where comments can be made on this entry
                        </entry>
                    </row>

                    <row>
                        <entry>
                            <methodname>getCommentFeedLink(string $type =
                                'atom'|'rss')</methodname>
                        </entry>

                        <entry>
                            Returns a <acronym>URI</acronym> pointing to a feed of the provided type
                            containing all comments for this entry (type defaults to
                            Atom/<acronym>RSS</acronym> depending on current feed type).
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </table>

        <para>
            The extended <acronym>API</acronym> for entries is identical to that for feeds with the
            exception of the Iterator methods which are not needed here.
        </para>

        <caution>
            <para>
                There is often confusion over the concepts of modified and
                created dates. In Atom, these are two clearly defined concepts
                (so knock yourself out) but in <acronym>RSS</acronym> they are vague.
                <acronym>RSS</acronym> 2.0
                defines a single <emphasis>&lt;pubDate&gt;</emphasis> element
                which typically refers to the date this entry was published,
                i.e. a creation date of sorts. This is not always the case, and
                it may change with updates or not. As a result, if you really
                want to check whether an entry has changed, don't rely on the
                results of <methodname>getDateModified()</methodname>. Instead,
                consider tracking the <acronym>MD5</acronym> hash of three other elements
                concatenated, e.g. using <methodname>getTitle()</methodname>,
                <methodname>getDescription()</methodname> and
                <methodname>getContent()</methodname>. If the entry was trully
                updated, this hash computation will give a different result than
                previously saved hashes for the same entry. Further muddying the
                waters, dates in feeds may follow different standards. Atom and
                Dublin Core dates should follow <acronym>ISO</acronym> 8601,
                and <acronym>RSS</acronym> dates should
                follow <acronym>RFC</acronym> 822 or <acronym>RFC</acronym> 2822
                which is also common. Date methods
                will throw an exception if <classname>Zend_Date</classname>
                cannot load the date string using one of the above standards.
            </para>
        </caution>

        <warning>
            <para>
                The values returned from these methods are not validated. This
                means users must perform validation on all retrieved data
                including the filtering of any <acronym>HTML</acronym> such as from
                <methodname>getContent()</methodname> before it is output from
                your application. Remember that most feeds come from external
                sources, and therefore the default assumption should be that
                they cannot be trusted.
            </para>
        </warning>

        <table>
            <title>Extended Entry Level API Methods</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry><methodname>getDomDocument()</methodname></entry>

                        <entry>
                            Returns the parent
                            <classname>DOMDocument</classname> object for the
                            entire feed (not just the current entry)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getElement()</methodname></entry>

                        <entry>
                            Returns the current entry level
                            <classname>DOMElement</classname> object
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getXpath()</methodname></entry>

                        <entry>
                            Returns the <classname>DOMXPath</classname> object
                            used internally to run queries on the
                            <classname>DOMDocument</classname> object (this
                            includes core and Extension namespaces
                            pre-registered)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getXpathPrefix()</methodname></entry>

                        <entry>
                            Returns the valid <acronym>DOM</acronym> path prefix prepended
                            to all XPath queries matching the entry being queried
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getEncoding()</methodname></entry>

                        <entry>
                            Returns the encoding of the source <acronym>XML</acronym> document
                            (note: this cannot account for errors such as the server sending
                            documents in a different encoding)
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getExtensions()</methodname></entry>

                        <entry>
                            Returns an array of all Extension objects loaded for
                            the current entry (note: both feed-level and entry-level
                            Extensions exist, and only entry-level Extensions are returned
                            here). The array keys are in the form {ExtensionName}_Entry.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getExtension(string $name)</methodname></entry>

                        <entry>
                            Returns an Extension object for the entry registered under the
                            provided name. This allows more fine-grained access to
                            Extensions which may otherwise be hidden within the implementation
                            of the standard <acronym>API</acronym> methods.
                        </entry>
                    </row>

                    <row>
                        <entry><methodname>getType()</methodname></entry>

                        <entry>
                            Returns a static class constant (e.g.
                            <constant>Zend_Feed_Reader::TYPE_ATOM_03</constant>,
                            i.e. Atom 0.3) indicating exactly what kind
                            of feed is being consumed.
                        </entry>
                    </row>
                </tbody>
            </tgroup>
        </table>
    </sect2>

    <sect2 id="zend.feed.reader.extending">
        <title>Extending Feed and Entry APIs</title>

        <para>
            Extending <classname>Zend_Feed_Reader</classname> allows you to add
            methods at both the feed and entry level which cover the retrieval
            of information not already supported by
            <classname>Zend_Feed_Reader</classname>. Given the number of
            <acronym>RSS</acronym> and
            Atom extensions that exist, this is a good thing since
            <classname>Zend_Feed_Reader</classname> couldn't possibly add
            everything.
        </para>

        <para>
            There are two types of Extensions possible, those which retrieve
            information from elements which are immediate children of the root
            element (e.g. <code>&lt;channel&gt;</code> for <acronym>RSS</acronym> or
            <code>&lt;feed&gt;</code> for Atom) and those who retrieve
            information from child elements of an entry (e.g.
            <code>&lt;item&gt;</code> for <acronym>RSS</acronym> or <code>&lt;entry&gt;</code> for
            Atom). On the filesystem these are grouped as classes within
            a namespace based on the extension standard's name. For
            example, internally we have
            <classname>Zend_Feed_Reader_Extension_DublinCore_Feed</classname>
            and <classname>Zend_Feed_Reader_Extension_DublinCore_Entry</classname>
            classes which are two Extensions implementing Dublin Core
            1.0/1.1 support.
        </para>

        <para>
            Extensions are loaded into <classname>Zend_Feed_Reader</classname>
            using <classname>Zend_Loader_PluginLoader</classname>, so their operation
            will be familiar from other Zend Framework components.
            <classname>Zend_Feed_Reader</classname> already bundles a number of
            these Extensions, however those which are not used internally and
            registered by default (so called Core Extensions) must be registered
            to <classname>Zend_Feed_Reader</classname> before they are used. The
            bundled Extensions include:
        </para>

        <table>
            <title>Core Extensions (pre-registered)</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry>DublinCore (Feed and Entry)</entry>

                        <entry>Implements support for Dublin Core Metadata Element Set 1.0
                        and 1.1 </entry>
                    </row>

                    <row>
                        <entry>Content (Entry only)</entry>

                        <entry>Implements support for Content 1.0</entry>
                    </row>

                    <row>
                        <entry>Atom (Feed and Entry)</entry>

                        <entry>Implements support for Atom 0.3 and Atom 1.0</entry>
                    </row>

                    <row>
                        <entry>Slash</entry>

                        <entry>Implements support for the Slash <acronym>RSS</acronym> 1.0 module</entry>
                    </row>

                    <row>
                        <entry>WellFormedWeb</entry>

                        <entry>Implements support for the Well Formed Web CommentAPI 1.0</entry>
                    </row>

                    <row>
                        <entry>Thread</entry>

                        <entry>Implements support for Atom Threading Extensions as described
                        in <acronym>RFC</acronym> 4685</entry>
                    </row>

                    <row>
                        <entry>Podcast</entry>

                        <entry>Implements support for the Podcast 1.0 <acronym>DTD</acronym> from Apple</entry>
                    </row>
                </tbody>
            </tgroup>
        </table>

        <para>
            The Core Extensions are somewhat special since they are extremely
            common and multi-faceted. For example, we have a Core Extension for Atom.
            Atom is implemented as an Extension (not just a base class) because it
            doubles as a valid <acronym>RSS</acronym> module - you can insert
            Atom elements into <acronym>RSS</acronym> feeds. I've even seen
            <acronym>RDF</acronym> feeds which use a lot of Atom in place of more
            common Extensions like Dublin Core.
        </para>

        <table>
            <title>Non-Core Extensions (must register manually)</title>

            <tgroup cols="2">
                <tbody>
                    <row>
                        <entry>Syndication</entry>
                        <entry>Implements Syndication 1.0 support for <acronym>RSS</acronym> feeds</entry>
                    </row>
                    <row>
                        <entry>CreativeCommons</entry>
                        <entry>A <acronym>RSS</acronym> module that adds an element at the &lt;channel&gt;
                        or &lt;item&gt; level that specifies which Creative Commons license
                        applies.</entry>
                    </row>
                </tbody>
            </tgroup>
        </table>

        <para>
            The additional non-Core Extensions are offered but not registered to
            <classname>Zend_Feed_Reader</classname> by default. If you want to
            use them, you'll need to tell
            <classname>Zend_Feed_Reader</classname> to load them in advance of
            importing a feed. Additional non-Core Extensions will be included
            in future iterations of the component.
        </para>

        <para>
            Registering an Extension with
            <classname>Zend_Feed_Reader</classname>, so it is loaded and its <acronym>API</acronym>
            is available to Feed and Entry objects, is a simple affair using the
            <classname>Zend_Loader_PluginLoader</classname>. Here we register
            the optional Slash Extension, and discover that it can be directly
            called from the Entry level <acronym>API</acronym> without any effort. Note that
            Extension names are case sensitive and use camel casing for multiple
            terms.
        </para>

        <programlisting language="php"><![CDATA[
Zend_Feed_Reader::registerExtension('Syndication');
$feed = Zend_Feed_Reader::import('http://rss.slashdot.org/Slashdot/slashdot');
$updatePeriod = $feed->current()->getUpdatePeriod();
]]></programlisting>

        <para>
            In the simple example above, we checked how frequently a feed is being updated
            using the <methodname>getUpdatePeriod()</methodname>
            method. Since it's not part of
            <classname>Zend_Feed_Reader</classname>'s core <acronym>API</acronym>, it could only be
            a method supported by the newly registered Syndication Extension.
        </para>

        <para>
            As you can also notice, the new methods from Extensions are accessible from the main
            <acronym>API</acronym> using <acronym>PHP</acronym>'s magic methods. As an alternative,
            you can also directly access any Extension object for a similar result as seen below.
        </para>

        <programlisting language="php"><![CDATA[
Zend_Feed_Reader::registerExtension('Syndication');
$feed = Zend_Feed_Reader::import('http://rss.slashdot.org/Slashdot/slashdot');
$syndication = $feed->getExtension('Syndication');
$updatePeriod = $syndication->getUpdatePeriod();
]]></programlisting>

        <sect3 id="zend.feed.reader.extending.feed">
            <title>Writing Zend_Feed_Reader Extensions</title>

            <para>
                Inevitably, there will be times when the
                <classname>Zend_Feed_Reader</classname> <acronym>API</acronym> is just not capable
                of getting something you need from a feed or entry. You can use
                the underlying source objects, like
                <classname>DOMDocument</classname>, to get these by hand however
                there is a more reusable method available by writing Extensions
                supporting these new queries.
            </para>

            <para>
                As an example, let's take the case of a purely fictitious
                corporation named Jungle Books. Jungle Books have been
                publishing a lot of reviews on books they sell (from external
                sources and customers), which are distributed as an <acronym>RSS</acronym> 2.0
                feed. Their marketing department realises that web applications
                using this feed cannot currently figure out exactly what book is
                being reviewed. To make life easier for everyone, they determine
                that the geek department needs to extend <acronym>RSS</acronym> 2.0 to include a
                new element per entry supplying the <acronym>ISBN</acronym>-10 or
                <acronym>ISBN</acronym>-13 number of
                the publication the entry concerns. They define the new
                <code>&lt;isbn&gt;</code> element quite simply with a standard
                name and namespace <acronym>URI</acronym>:
            </para>

            <programlisting language="php"><![CDATA[
JungleBooks 1.0:
http://example.com/junglebooks/rss/module/1.0/
]]></programlisting>

            <para>
                A snippet of <acronym>RSS</acronym> containing this extension in practice could be
                something similar to:
            </para>

            <programlisting language="php"><![CDATA[
<?xml version="1.0" encoding="utf-8" ?>
<rss version="2.0"
   xmlns:content="http://purl.org/rss/1.0/modules/content/"
   xmlns:jungle="http://example.com/junglebooks/rss/module/1.0/">
<channel>
    <title>Jungle Books Customer Reviews</title>
    <link>http://example.com/junglebooks</link>
    <description>Many book reviews!</description>
    <pubDate>Fri, 26 Jun 2009 19:15:10 GMT</pubDate>
    <jungle:dayPopular>http://example.com/junglebooks/book/938</jungle:dayPopular>
    <item>
        <title>Review Of Flatland: A Romance of Many Dimensions</title>
        <link>http://example.com/junglebooks/review/987</link>
        <author>Confused Physics Student</author>
        <content:encoded>
        A romantic square?!
        </content:encoded>
        <pubDate>Thu, 25 Jun 2009 20:03:28 -0700</pubDate>
        <jungle:isbn>048627263X</jungle:isbn>
    </item>
</channel>
</rss>
]]></programlisting>

            <para>
                Implementing this new <acronym>ISBN</acronym> element as a simple entry level
                extension would require the following class (using your own class
                namespace outside of Zend).
            </para>

            <programlisting language="php"><![CDATA[
class My_FeedReader_Extension_JungleBooks_Entry
    extends Zend_Feed_Reader_Extension_EntryAbstract
{
    public function getIsbn()
    {
        if (isset($this->_data['isbn'])) {
            return $this->_data['isbn'];
        }
        $isbn = $this->_xpath->evaluate(
            'string(' . $this->getXpathPrefix() . '/jungle:isbn)'
        );
        if (!$isbn) {
            $isbn = null;
        }
        $this->_data['isbn'] = $isbn;
        return $this->_data['isbn'];
    }

    protected function _registerNamespaces()
    {
        $this->_xpath->registerNamespace(
            'jungle', 'http://example.com/junglebooks/rss/module/1.0/'
        );
    }
}
]]></programlisting>

            <para>
                This extension is easy enough to follow. It creates a new method
                <methodname>getIsbn()</methodname> which runs an XPath query on
                the current entry to extract the <acronym>ISBN</acronym> number enclosed by the
                <code>&lt;jungle:isbn&gt;</code> element. It can optionally
                store this to the internal non-persistent cache (no need to keep
                querying the <acronym>DOM</acronym> if it's called again on the same entry). The
                value is returned to the caller. At the end we have a protected
                method (it's abstract so it must exist) which registers the
                Jungle Books namespace for their custom <acronym>RSS</acronym> module. While we
                call this an <acronym>RSS</acronym> module, there's nothing to prevent the same
                element being used in Atom feeds - and all Extensions which use
                the prefix provided by <methodname>getXpathPrefix()</methodname>
                are actually neutral and work on <acronym>RSS</acronym> or Atom feeds with no
                extra code.
            </para>

            <para>
                Since this Extension is stored outside of Zend Framework, you'll
                need to register the path prefix for your Extensions so
                <classname>Zend_Loader_PluginLoader</classname> can find them.
                After that, it's merely a matter of registering the Extension,
                if it's not already loaded, and using it in practice.
            </para>

            <programlisting language="php"><![CDATA[
if(!Zend_Feed_Reader::isRegistered('JungleBooks')) {
    Zend_Feed_Reader::addPrefixPath(
        '/path/to/My/FeedReader/Extension', 'My_FeedReader_Extension'
    );
    Zend_Feed_Reader::registerExtension('JungleBooks');
}
$feed = Zend_Feed_Reader::import('http://example.com/junglebooks/rss');

// ISBN for whatever book the first entry in the feed was concerned with
$firstIsbn = $feed->current()->getIsbn();
]]></programlisting>

            <para>
                Writing a feed level Extension is not much different. The
                example feed from earlier included an unmentioned
                <code>&lt;jungle:dayPopular&gt;</code> element which Jungle
                Books have added to their standard to include a link to the
                day's most popular book (in terms of visitor traffic). Here's
                an Extension which adds a
                <methodname>getDaysPopularBookLink()</methodname> method to the
                feel level <acronym>API</acronym>.
            </para>

            <programlisting language="php"><![CDATA[
class My_FeedReader_Extension_JungleBooks_Feed
    extends Zend_Feed_Reader_Extension_FeedAbstract
{
    public function getDaysPopularBookLink()
    {
        if (isset($this->_data['dayPopular'])) {
            return $this->_data['dayPopular'];
        }
        $dayPopular = $this->_xpath->evaluate(
            'string(' . $this->getXpathPrefix() . '/jungle:dayPopular)'
        );
        if (!$dayPopular) {
            $dayPopular = null;
        }
        $this->_data['dayPopular'] = $dayPopular;
        return $this->_data['dayPopular'];
    }

    protected function _registerNamespaces()
    {
        $this->_xpath->registerNamespace(
            'jungle', 'http://example.com/junglebooks/rss/module/1.0/'
        );
    }
}
]]></programlisting>

            <para>
                Let's repeat the last example using a custom Extension to show the
                method being used.
            </para>

            <programlisting language="php"><![CDATA[
if(!Zend_Feed_Reader::isRegistered('JungleBooks')) {
    Zend_Feed_Reader::addPrefixPath(
        '/path/to/My/FeedReader/Extension', 'My_FeedReader_Extension'
    );
    Zend_Feed_Reader::registerExtension('JungleBooks');
}
$feed = Zend_Feed_Reader::import('http://example.com/junglebooks/rss');

// URI to the information page of the day's most popular book with visitors
$daysPopularBookLink = $feed->getDaysPopularBookLink();

// ISBN for whatever book the first entry in the feed was concerned with
$firstIsbn = $feed->current()->getIsbn();
]]></programlisting>

            <para>
                Going through these examples, you'll note that we don't register
                feed and entry Extensions separately. Extensions within the same
                standard may or may not include both a feed and entry class, so
                <classname>Zend_Feed_Reader</classname> only requires you to
                register the overall parent name, e.g. JungleBooks, DublinCore,
                Slash. Internally, it can check at what level Extensions exist
                and load them up if found. In our case, we have a full set of
                Extensions now: <classname>JungleBooks_Feed</classname> and
                <classname>JungleBooks_Entry</classname>.
            </para>
        </sect3>
  </sect2>
</sect1>