Fonction key()  
Fait référence à une relation définie avec un élément <xsl:key>. Théoriquement, la fonction key() fonctionne de la même manière que la fonction id(), bien que les clés soient plus flexibles que les ID.
 
Entrées

Le nom de la clé (définie par un élément <xsl:key>) et un objet. Si l'objet est un ensemble de nœuds, la fonction key() s'applique alors à elle-même la valeur de chaîne de chacun des nœuds de l'ensemble et renvoie l'ensemble de nœuds résultant de toutes les invocations de cette fonction key(). Si l'objet est de n'importe quel autre type, il est converti en chaîne comme si la fonction string() avait été appelée.

 
Sortie

Un ensemble de nœuds contenant les nœuds dans le même document que celui du nœud de contexte dont les valeurs de la clé recherchée correspondent aux arguments de la recherche. En d'autres termes, si la feuille de style contient un élément <xsl:key> qui définit une clé nommée postalcodes à partir de l'enfant <postalcode> de tous les éléments <address> dans le document actuel, l'appel de la fonction key(postalcodes, '34829') renvoie un ensemble de nœuds contenant tous les éléments <address> ayant un élément <postalcode> dont la valeur est 34829.
 
Définie dans

XSLT section 12.2, Clés.
 
Exemple

Pour montrer les performances de la fonction key(), nous utiliserons la version de document tronquée du glossaire déjà mentionnée dans le chapitre 5:

<?xml version="1.0"?>
<glossary>
  <glentry>
    <term id="applet">applet</term>
    <defn topic="Java" language="en">
      An application program,
      written in the Java programming language, that can be 
      retrieved from a web server and executed by a web browser. 
      A reference to an applet appears in the markup for a web 
      page, in the same way that a reference to a graphics
      file appears; a browser retrieves an applet in the same 
      way that it retrieves a graphics file. 
      For security reasons, an applet's access rights are limited
      in two ways: the applet cannot access the filesystem of the 
      client upon which it is executing, and the applet's 
      communication across the network is limited to the server 
      from which it was downloaded. 
      Contrast with <xref refid="servlet"/>.
    </defn>

    <defn topic="Java" language="it">
      [Pretend this is an Italian definition of applet.]
    </defn>
    <defn topic="Java" language="es">
      [Pretend this is a Spanish definition of applet.]
    </defn>
  </glentry>

  <glentry>
    <term id="DMZlong" xreftext="demilitarized zone">demilitarized 
      zone (DMZ)</term>
    <defn topic="security" language="en">
      In network security, a network that is isolated from, and 
      serves as a neutral zone between, a trusted network (for example, 
      a private intranet) and an untrusted network (for example, the
      Internet). One or more secure gateways usually control access 
      to the DMZ from the trusted or the untrusted network.
    </defn>
    <defn topic="security" language="it">
      [Pretend this is an Italian definition of DMZ.]
    </defn>
    <defn topic="security" language="es">
      [Pretend this is a Spanish definition of DMZ.]
    </defn>
    <defn topic="security" language="jp">
      [Pretend this is a Japanese definition of DMZ.]
    </defn>
    <defn topic="security" language="de">
      [Pretend this is a German definition of DMZ.]
    </defn>
  </glentry>

  <glentry>
    <term id="servlet">servlet</term>
    <defn topic="Java" language="en">
      An application program, written in the Java programming language, 
      that is executed on a web server. A reference to a servlet 
      appears in the markup for a web page, in the same way that a 
      reference to a graphics file appears. The web server executes
      the servlet and sends the results of the execution (if there are
      any) to the web browser. Contrast with <xref refid="applet" />.
    </defn>
    <defn topic="Java" language="es">
      [Pretend this is a Spanish definition of servlet.]
    </defn>
    <defn topic="Java" language="it">
      [Pretend this is an Italian definition of servlet.]
    </defn>

    <defn topic="Java" language="de">
      [Pretend this is a German definition of servlet.]
    </defn>
    <defn topic="Java" language="jp">
      [Pretend this is a Japanese definition of servlet.]
    </defn>
  </glentry>
</glossary>

La feuille de style utilisée pour traiter ce document est la suivante : Notez que deux éléments <xsl:key> ont été définis afin de pouvoir indexer le document XML de deux manières différentes :

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html" indent="yes"/>
<xsl:strip-space elements="*"/>

  <xsl:key name="language-index" match="defn" use="@language"/>
  <xsl:key name="term-ids"       match="term" use="@id"/>

  <xsl:param name="targetLanguage"/>

  <xsl:template match="/">
    <xsl:apply-templates select="glossary"/>
  </xsl:template>

  <xsl:template match="glossary">
    <html>
      <head>
        <title>
          <xsl:text>Glossary Listing: </xsl:text>
        </title>
      </head>
      <body>
        <h1>
          <xsl:text>Glossary Listing: </xsl:text>
        </h1>
        <xsl:for-each select="key('language-index', $targetLanguage)">
          <xsl:apply-templates select="ancestor::glentry"/>
        </xsl:for-each>
      </body>
    </html>
  </xsl:template>

  <xsl:template match="glentry">
    <p>
      <b>
        <a>
          <xsl:attribute name="name">
            <xsl:value-of select="term/@id" />
          </xsl:attribute>
        </a>
        <xsl:value-of select="term"/>
        <xsl:text>: </xsl:text>
      </b>
      <xsl:apply-templates select="defn[@language=$targetLanguage]"/>
    </p>
  </xsl:template>

  <xsl:template match="defn">
    <xsl:apply-templates 
     select="*|comment()|processing-instruction()|text()"/>
  </xsl:template>

  <xsl:template match="xref">
    <a>
      <xsl:attribute name="href">
        <xsl:text>#</xsl:text><xsl:value-of select="@refid"/>
      </xsl:attribute>
      <xsl:choose>
        <xsl:when test="key('term-ids', @refid)[1]/@xreftext">
          <xsl:value-of select="key('term-ids', @refid)[1]/@xreftext"/>
        </xsl:when>
        <xsl:otherwise>
          <xsl:value-of select="key('term-ids', @refid)[1]"/>
        </xsl:otherwise>
      </xsl:choose>
    </a>
  </xsl:template>

</xsl:stylesheet>

Transformer le glossaire avec un targetLanguage de en donne les résultats suivants :

<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Glossary Listing: </title>
</head>
<body>
<h1>Glossary Listing: </h1>
<p>
<b><a name="applet"></a>applet: </b>
      An application program,
      written in the Java programming language, that can be 
      retrieved from a web server and executed by a web browser. 
      A reference to an applet appears in the markup for a web 
      page, in the same way that a reference to a graphics
      file appears; a browser retrieves an applet in the same 
      way that it retrieves a graphics file. 
      For security reasons, an applet's access rights are limited
      in two ways: the applet cannot access the filesystem of the 
      client upon which it is executing, and the applet's 
      communication across the network is limited to the server 
      from which it was downloaded. 
      Contrast with <a href="#servlet">servlet</a>.
    </p>
<p>
<b><a name="DMZlong"></a>demilitarized 
      zone (DMZ): </b>
      In network security, a network that is isolated from, and 
      serves as a neutral zone between, a trusted network (for example, 
      a private intranet) and an untrusted network (for example, the
      Internet). One or more secure gateways usually control access 
      to the DMZ from the trusted or the untrusted network.
    </p>
<p>
<b><a name="servlet"></a>servlet: </b>
      An application program, written in the Java programming language, 
      that is executed on a web server. A reference to a servlet 
      appears in the markup for a web page, in the same way that a 
      reference to a graphics file appears. The web server executes
      the servlet and sends the results of the execution (if there are
      any) to the web browser. Contrast with <a href="#applet">applet</a>.
    </p>
</body>
</html>

La Figure C-5 montre l'aspect qu'aurait le document une fois affiché dans un navigateur. Utiliser un targetLanguage de jp donne alors les résultats suivants :

Glossaire HTML généré

<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Glossary Listing: </title>
</head>
<body>
<h1>Glossary Listing: </h1>
<p>
<b><a name="DMZlong"></a>demilitarized 
      zone (DMZ): </b>
      [Pretend this is a Japanese definition of DMZ.]
    </p>
<p>
<b><a name="servlet"></a>servlet: </b>
      [Pretend this is a Japanese definition of servlet.]
    </p>
</body>
</html>
      </programlisting>

Une fois affiché, le document ressemble à la Figure C-6. Notez que les résultats sont totalement différents en cas de modification du targetLanguage.

Glossaire HTML généré