539 lines
17 KiB
XML
539 lines
17 KiB
XML
<!--
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__ __ _
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___\ \/ /_ __ __ _| |_
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/ _ \\ /| '_ \ / _` | __|
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| __// \| |_) | (_| | |_
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\___/_/\_\ .__/ \__,_|\__|
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|_| XML parser
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Copyright (c) 2001 Scott Bronson <bronson@rinspin.com>
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Copyright (c) 2002-2003 Fred L. Drake, Jr. <fdrake@users.sourceforge.net>
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Copyright (c) 2009 Karl Waclawek <karl@waclawek.net>
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Copyright (c) 2016-2022 Sebastian Pipping <sebastian@pipping.org>
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Copyright (c) 2016 Ardo van Rangelrooij <ardo@debian.org>
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Copyright (c) 2017 Rhodri James <rhodri@wildebeest.org.uk>
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Copyright (c) 2020 Joe Orton <jorton@redhat.com>
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Copyright (c) 2021 Tim Bray <tbray@textuality.com>
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Unlike most of Expat,
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this file is copyrighted under the GNU Free Documentation License 1.1.
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-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
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<!ENTITY dhfirstname "<firstname>Scott</firstname>">
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<!ENTITY dhsurname "<surname>Bronson</surname>">
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<!ENTITY dhdate "<date>March 4, 2022</date>">
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<!-- Please adjust this^^ date whenever cutting a new release. -->
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<!ENTITY dhsection "<manvolnum>1</manvolnum>">
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<!ENTITY dhemail "<email>bronson@rinspin.com</email>">
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<!ENTITY dhusername "Scott Bronson">
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<!ENTITY dhucpackage "<refentrytitle>XMLWF</refentrytitle>">
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<!ENTITY dhpackage "xmlwf">
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<!ENTITY debian "<productname>Debian GNU/Linux</productname>">
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<!ENTITY gnu "<acronym>GNU</acronym>">
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]>
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<refentry>
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<refentryinfo>
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<address>
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&dhemail;
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</address>
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<author>
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&dhfirstname;
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&dhsurname;
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</author>
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<copyright>
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<year>2001</year>
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<holder>&dhusername;</holder>
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</copyright>
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&dhdate;
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</refentryinfo>
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<refmeta>
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&dhucpackage;
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&dhsection;
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</refmeta>
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<refnamediv>
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<refname>&dhpackage;</refname>
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<refpurpose>Determines if an XML document is well-formed</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>&dhpackage;</command>
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<arg><replaceable>OPTIONS</replaceable></arg>
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<arg><replaceable>FILE</replaceable> ...</arg>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>&dhpackage;</command>
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<arg choice="plain"><option>-h</option></arg>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>&dhpackage;</command>
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<arg choice="plain"><option>-v</option></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>DESCRIPTION</title>
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<para>
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<command>&dhpackage;</command> uses the Expat library to
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determine if an XML document is well-formed. It is
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non-validating.
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</para>
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<para>
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If you do not specify any files on the command-line, and you
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have a recent version of <command>&dhpackage;</command>, the
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input file will be read from standard input.
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</para>
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</refsect1>
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<refsect1>
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<title>WELL-FORMED DOCUMENTS</title>
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<para>
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A well-formed document must adhere to the
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following rules:
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</para>
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<itemizedlist>
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<listitem><para>
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The file begins with an XML declaration. For instance,
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<literal><?xml version="1.0" standalone="yes"?></literal>.
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<emphasis>NOTE</emphasis>:
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<command>&dhpackage;</command> does not currently
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check for a valid XML declaration.
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</para></listitem>
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<listitem><para>
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Every start tag is either empty (<tag/>)
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or has a corresponding end tag.
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</para></listitem>
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<listitem><para>
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There is exactly one root element. This element must contain
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all other elements in the document. Only comments, white
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space, and processing instructions may come after the close
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of the root element.
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</para></listitem>
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<listitem><para>
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All elements nest properly.
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</para></listitem>
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<listitem><para>
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All attribute values are enclosed in quotes (either single
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or double).
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</para></listitem>
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</itemizedlist>
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<para>
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If the document has a DTD, and it strictly complies with that
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DTD, then the document is also considered <emphasis>valid</emphasis>.
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<command>&dhpackage;</command> is a non-validating parser --
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it does not check the DTD. However, it does support
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external entities (see the <option>-x</option> option).
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</para>
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</refsect1>
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<refsect1>
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<title>OPTIONS</title>
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<para>
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When an option includes an argument, you may specify the argument either
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separately ("<option>-d</option> <replaceable>output</replaceable>") or concatenated with the
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option ("<option>-d</option><replaceable>output</replaceable>"). <command>&dhpackage;</command>
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supports both.
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</para>
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<variablelist>
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<varlistentry>
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<term><option>-a</option> <replaceable>factor</replaceable></term>
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<listitem>
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<para>
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Sets the maximum tolerated amplification factor
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for protection against billion laughs attacks (default: 100.0).
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The amplification factor is calculated as ..
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</para>
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<literallayout>
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amplification := (direct + indirect) / direct
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</literallayout>
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<para>
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.. while parsing, whereas
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<direct> is the number of bytes read
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from the primary document in parsing and
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<indirect> is the number of bytes
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added by expanding entities and reading of external DTD files,
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combined.
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</para>
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<para>
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<emphasis>NOTE</emphasis>:
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If you ever need to increase this value for non-attack payload,
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please file a bug report.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-b</option> <replaceable>bytes</replaceable></term>
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<listitem>
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<para>
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Sets the number of output bytes (including amplification)
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needed to activate protection against billion laughs attacks
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(default: 8 MiB).
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This can be thought of as an "activation threshold".
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</para>
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<para>
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<emphasis>NOTE</emphasis>:
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If you ever need to increase this value for non-attack payload,
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please file a bug report.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-c</option></term>
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<listitem>
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<para>
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If the input file is well-formed and <command>&dhpackage;</command>
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doesn't encounter any errors, the input file is simply copied to
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the output directory unchanged.
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This implies no namespaces (turns off <option>-n</option>) and
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requires <option>-d</option> to specify an output directory.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-d</option> <replaceable>output-dir</replaceable></term>
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<listitem>
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<para>
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Specifies a directory to contain transformed
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representations of the input files.
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By default, <option>-d</option> outputs a canonical representation
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(described below).
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You can select different output formats using <option>-c</option>,
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<option>-m</option> and <option>-N</option>.
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</para>
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<para>
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The output filenames will
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be exactly the same as the input filenames or "STDIN" if the input is
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coming from standard input. Therefore, you must be careful that the
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output file does not go into the same directory as the input
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file. Otherwise, <command>&dhpackage;</command> will delete the
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input file before it generates the output file (just like running
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<literal>cat < file > file</literal> in most shells).
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</para>
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<para>
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Two structurally equivalent XML documents have a byte-for-byte
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identical canonical XML representation.
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Note that ignorable white space is considered significant and
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is treated equivalently to data.
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More on canonical XML can be found at
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http://www.jclark.com/xml/canonxml.html .
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-e</option> <replaceable>encoding</replaceable></term>
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<listitem>
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<para>
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Specifies the character encoding for the document, overriding
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any document encoding declaration. <command>&dhpackage;</command>
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supports four built-in encodings:
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<literal>US-ASCII</literal>,
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<literal>UTF-8</literal>,
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<literal>UTF-16</literal>, and
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<literal>ISO-8859-1</literal>.
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Also see the <option>-w</option> option.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-k</option></term>
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<listitem>
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<para>
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When processing multiple files, <command>&dhpackage;</command>
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by default halts after the the first file with an error.
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This tells <command>&dhpackage;</command> to report the error
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but to keep processing.
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This can be useful, for example, when testing a filter that converts
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many files to XML and you want to quickly find out which conversions
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failed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-m</option></term>
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<listitem>
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<para>
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Outputs some strange sort of XML file that completely
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describes the input file, including character positions.
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Requires <option>-d</option> to specify an output file.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-n</option></term>
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<listitem>
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<para>
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Turns on namespace processing. (describe namespaces)
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<option>-c</option> disables namespaces.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-N</option></term>
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<listitem>
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<para>
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Adds a doctype and notation declarations to canonical XML output.
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This matches the example output used by the formal XML test cases.
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Requires <option>-d</option> to specify an output file.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-p</option></term>
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<listitem>
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<para>
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Tells <command>&dhpackage;</command> to process external DTDs and parameter
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entities.
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</para>
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<para>
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Normally <command>&dhpackage;</command> never parses parameter
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entities. <option>-p</option> tells it to always parse them.
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<option>-p</option> implies <option>-x</option>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-r</option></term>
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<listitem>
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<para>
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Normally <command>&dhpackage;</command> memory-maps the XML file
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before parsing; this can result in faster parsing on many
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platforms.
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<option>-r</option> turns off memory-mapping and uses normal file
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IO calls instead.
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Of course, memory-mapping is automatically turned off
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when reading from standard input.
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</para>
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<para>
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Use of memory-mapping can cause some platforms to report
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substantially higher memory usage for
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<command>&dhpackage;</command>, but this appears to be a matter of
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the operating system reporting memory in a strange way; there is
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not a leak in <command>&dhpackage;</command>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-s</option></term>
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<listitem>
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<para>
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Prints an error if the document is not standalone.
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A document is standalone if it has no external subset and no
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references to parameter entities.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-t</option></term>
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<listitem>
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<para>
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Turns on timings. This tells Expat to parse the entire file,
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but not perform any processing.
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This gives a fairly accurate idea of the raw speed of Expat itself
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without client overhead.
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<option>-t</option> turns off most of the output options
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(<option>-d</option>, <option>-m</option>, <option>-c</option>, ...).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-v</option></term>
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<listitem>
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<para>
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Prints the version of the Expat library being used, including some
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information on the compile-time configuration of the library, and
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then exits.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-w</option></term>
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<listitem>
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<para>
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Enables support for Windows code pages.
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Normally, <command>&dhpackage;</command> will throw an error if it
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runs across an encoding that it is not equipped to handle itself. With
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<option>-w</option>, <command>&dhpackage;</command> will try to use a Windows code
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page. See also <option>-e</option>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-x</option></term>
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<listitem>
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<para>
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Turns on parsing external entities.
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</para>
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<para>
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Non-validating parsers are not required to resolve external
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entities, or even expand entities at all.
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Expat always expands internal entities (?),
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but external entity parsing must be enabled explicitly.
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</para>
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<para>
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External entities are simply entities that obtain their
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data from outside the XML file currently being parsed.
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</para>
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<para>
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This is an example of an internal entity:
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<literallayout>
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<!ENTITY vers '1.0.2'>
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</literallayout>
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</para>
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<para>
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And here are some examples of external entities:
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<literallayout>
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<!ENTITY header SYSTEM "header-&vers;.xml"> (parsed)
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<!ENTITY logo SYSTEM "logo.png" PNG> (unparsed)
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</literallayout>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--</option></term>
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<listitem>
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<para>
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(Two hyphens.)
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Terminates the list of options. This is only needed if a filename
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starts with a hyphen. For example:
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</para>
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<literallayout>
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&dhpackage; -- -myfile.xml
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</literallayout>
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<para>
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will run <command>&dhpackage;</command> on the file
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<filename>-myfile.xml</filename>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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Older versions of <command>&dhpackage;</command> do not support
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reading from standard input.
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</para>
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</refsect1>
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<refsect1>
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<title>OUTPUT</title>
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<para>
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<command>&dhpackage;</command> outputs nothing for files which are problem-free.
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If any input file is not well-formed, or if the output for any
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input file cannot be opened, <command>&dhpackage;</command> prints a single
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line describing the problem to standard output.
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</para>
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<para>
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If the <option>-k</option> option is not provided, <command>&dhpackage;</command>
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halts upon encountering a well-formedness or output-file error.
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If <option>-k</option> is provided, <command>&dhpackage;</command> continues
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processing the remaining input files, describing problems found with any of them.
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</para>
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</refsect1>
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<refsect1>
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<title>EXIT STATUS</title>
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<para>For option <option>-v</option> or <option>-h</option>, <command>&dhpackage;</command> always exits with status code 0. For other cases, the following exit status codes are returned:
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<variablelist>
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<varlistentry>
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<term><option>0</option></term>
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<listitem><para>The input files are well-formed and the output (if requested) was written successfully.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>1</option></term>
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<listitem><para>An internal error occurred.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>2</option></term>
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<listitem><para>One or more input files were not well-formed or could not be parsed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>3</option></term>
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<listitem><para>If using the <option>-d</option> option, an error occurred opening an output file.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>4</option></term>
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<listitem><para>There was a command-line argument error in how <command>&dhpackage;</command> was invoked.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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|
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<refsect1>
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<title>BUGS</title>
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<para>
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The errors should go to standard error, not standard output.
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</para>
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<para>
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There should be a way to get <option>-d</option> to send its
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output to standard output rather than forcing the user to send
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it to a file.
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</para>
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<para>
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I have no idea why anyone would want to use the
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<option>-d</option>, <option>-c</option>, and
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<option>-m</option> options. If someone could explain it to
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me, I'd like to add this information to this manpage.
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</para>
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</refsect1>
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<refsect1>
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<title>SEE ALSO</title>
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<para>
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<literallayout>
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The Expat home page: https://libexpat.github.io/
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The W3 XML 1.0 specification (fourth edition): https://www.w3.org/TR/2006/REC-xml-20060816/
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Billion laughs attack: https://en.wikipedia.org/wiki/Billion_laughs_attack
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</literallayout>
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</para>
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</refsect1>
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<refsect1>
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<title>AUTHOR</title>
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<para>
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This manual page was originally written by &dhusername; &dhemail;
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in December 2001 for
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the &debian; system (but may be used by others). Permission is
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granted to copy, distribute and/or modify this document under
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the terms of the <acronym>GNU</acronym> Free Documentation
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License, Version 1.1.
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</para>
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</refsect1>
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</refentry>
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