</listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">version</replaceable></term>
      <listitem>
       <para>
        The version of the extension to install.  This can be written as
        either an identifier or a string literal.  The default version is
        whatever is specified in the extension's control file.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>CASCADE</literal></term>
      <listitem>
       <para>
        Automatically install any extensions that this extension depends on
        that are not already installed.  Their dependencies are likewise
        automatically installed, recursively.  The <literal>SCHEMA</literal> clause,
        if given, applies to all extensions that get installed this way.
        Other options of the statement are not applied to
        automatically-installed extensions; in particular, their default
        versions are always selected.
       </para>
      </listitem>
     </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   Before you can use <command>CREATE EXTENSION</command> to load an extension
   into a database, the extension's supporting files must be installed.
   Information about installing the extensions supplied with
   <productname>PostgreSQL</productname> can be found in
   <link linkend="contrib">Additional Supplied Modules</link>.
  </para>

  <para>
   The extensions currently available for loading can be identified from the
   <link linkend="view-pg-available-extensions"><structname>pg_available_extensions</structname></link>
   or
   <link linkend="view-pg-available-extension-versions"><structname>pg_available_extension_versions</structname></link>
   system views.
  </para>

  <caution>
   <para>
    Installing an extension as superuser requires trusting that the
    extension's author wrote the extension installation script in a secure
    fashion.  It is not terribly difficult for a malicious user to create
    trojan-horse objects