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https://github.com/sigmasternchen/php-doc-en
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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@146902 c90b9560-bf6c-de11-be94-00142212c4b1
205 lines
7.3 KiB
XML
205 lines
7.3 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.11 $ -->
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<!-- splitted from ./en/functions/sockets.xml, last change in rev 1.27 -->
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<refentry id="function.socket-select">
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<refnamediv>
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<refname>socket_select</refname>
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<refpurpose>
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Runs the select() system call on the given arrays of sockets
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with a specified timeout
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</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>int</type><methodname>socket_select</methodname>
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<methodparam><type>array</type><parameter>&read</parameter></methodparam>
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<methodparam><type>array</type><parameter>&write</parameter></methodparam>
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<methodparam><type>array</type><parameter>&except</parameter></methodparam>
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<methodparam><type>int</type><parameter>tv_sec</parameter></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>tv_usec</parameter></methodparam>
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</methodsynopsis>
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&warn.experimental.func;
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<para>
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<function>socket_select</function> accepts arrays of sockets and
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waits for them to change status. Those coming with BSD sockets background
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will recognize that those socket resource arrays are in fact the
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so-called file descriptor sets. Three independent arrays of socket
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resources are watched.
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</para>
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<para>
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The sockets listed in the <parameter>read</parameter> array will be watched to
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see if characters become available for reading (more precisely, to see if
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a read will not block - in particular, a socket resource is also ready on
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end-of-file, in which case a <function>socket_read</function> will return
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a zero length string).
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</para>
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<para>
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The sockets listed in the <parameter>write</parameter> array will be
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watched to see if a write will not block.
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</para>
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<para>
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The sockets listed in the <parameter>except</parameter> array will be
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watched for exceptions.
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</para>
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<warning>
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<para>
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On exit, the arrays are modified to indicate which socket resource
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actually changed status.
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</para>
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</warning>
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<para>
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You do not need to pass every array to
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<function>socket_select</function>. You can leave it out and use an
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empty array or &null; instead. Also do not forget that those arrays are
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passed <emphasis>by reference</emphasis> and will be modified after
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<function>socket_select</function> returns.
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</para>
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<para>
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<example>
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<title><function>socket_select</function> example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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/* Prepare the read array */
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$read = array($socket1, $socket2);
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$num_changed_sockets = socket_select($read, $write = NULL, $except = NULL, 0);
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if ($num_changed_sockets === false) {
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/* Error handling */
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} else if ($num_changed_sockets > 0) {
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/* At least at one of the sockets something interesting happened */
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}
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<note>
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<para>
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Due a limitation in the current Zend Engine it is not possible to pass a
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constant modifier like &null; directly as a parameter to a function
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which expects this parameter to be passed by reference. Instead use a
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temporary variable or an expression with the leftmost member being a
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temporary variable:
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<example>
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<title>Using &null; with <function>socket_select</function></title>
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<programlisting role="php">
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<![CDATA[
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<?php
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socket_select($r, $w, $e = NULL, 0);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</note>
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<para>
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The <parameter>tv_sec</parameter> and <parameter>tv_usec</parameter>
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together form the <emphasis>timeout</emphasis> parameter. The
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<emphasis>timeout</emphasis> is an upper bound on the amount of time
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elapsed before <function>socket_select</function> return.
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<parameter>tv_sec</parameter> may be zero , causing
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<function>socket_select</function> to return immediately. This is useful
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for polling. If <parameter>tv_sec</parameter> is &null; (no timeout),
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<function>socket_select</function> can block indefinitely.
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</para>
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<para>
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On success <function>socket_select</function> returns the number of
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socket resources contained in the modified arrays, which may be zero if
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the timeout expires before anything interesting happens. On error &false;
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is returned. The error code can be retrieved with
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<function>socket_last_error</function>.
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</para>
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<note>
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<para>
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Be sure to use the <literal>===</literal> operator when checking for an
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error. Since the <function>socket_select</function> may return 0 the
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comparison with <literal>==</literal> would evaluate to &true;:
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<example>
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<title>Understanding <function>socket_select</function>'s result</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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if (false === socket_select($r, $w, $e = NULL, 0)) {
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echo "socket_select() failed, reason: " .
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socket_strerror(socket_last_error()) . "\n";
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}
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</note>
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<note>
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<para>
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Be aware that some socket implementations need to be handled very
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carefully. A few basic rules:
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<itemizedlist>
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<listitem>
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<simpara>
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You should always try to use <function>socket_select</function>
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without timeout. Your program should have nothing to do if there is
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no data available. Code that depends on timeouts is not usually
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portable and difficult to debug.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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No socket resource must be added to any set if you do not intend to
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check its result after the <function>socket_select</function> call,
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and respond appropriately. After <function>socket_select</function>
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returns, all socket resources in all arrays must be checked. Any
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socket resource that is available for writing must be written to, and
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any socket resource available for reading must be read from.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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If you read/write to a socket returns in the arrays be aware that
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they do not necessarily read/write the full amount of data you have
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requested. Be prepared to even only be able to read/write a single
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byte.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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It's common to most socket implementations that the only exception
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caught with the <parameter>except</parameter> array is out-of-bound
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data received on a socket.
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</simpara>
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</listitem>
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</itemizedlist>
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</para>
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</note>
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<para>
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See also
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<function>socket_read</function>,
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<function>socket_write</function>,
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<function>socket_last_error</function> and
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<function>socket_strerror</function>.
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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