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* doc/site.xsl doc/*.html doc/Makefile.am: now autogenerate the web site from the main HTML document. Daniel
128 lines
7.1 KiB
HTML
128 lines
7.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
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<html>
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<head>
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<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type">
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<style type="text/css"><!--
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TD {font-size: 10pt; font-family: Verdana,Arial,Helvetica}
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BODY {font-size: 10pt; font-family: Verdana,Arial,Helvetica; margin-top: 5pt; margin-left: 0pt; margin-right: 0pt}
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H1 {font-size: 16pt; font-family: Verdana,Arial,Helvetica}
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H2 {font-size: 14pt; font-family: Verdana,Arial,Helvetica}
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H3 {font-size: 12pt; font-family: Verdana,Arial,Helvetica}
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--></style>
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<title>Entities or no entities</title>
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</head>
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<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000">
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<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr>
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<td width="180">
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<a href="http://www.gnome.org/"><img src="smallfootonly.gif" alt="Gnome Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a>
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</td>
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<td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center">
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<h1>The XML C library for Gnome</h1>
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<h2>Entities or no entities</h2>
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</td></tr></table></td></tr></table></td>
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</tr></table>
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<table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr>
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<td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3">
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<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
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<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt">
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<li><a href="index.html">Home</a></li>
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<li><a href="FAQ.html">FAQ</a></li>
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<li><a href="intro.html">Introduction</a></li>
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<li><a href="docs.html">Documentation</a></li>
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<li><a href="bugs.html">Reporting bugs and getting help</a></li>
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<li><a href="help.html">How to help</a></li>
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<li><a href="downloads.html">Downloads</a></li>
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<li><a href="news.html">News</a></li>
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<li><a href="XML.html">XML</a></li>
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<li><a href="XSLT.html">XSLT</a></li>
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<li><a href="architecture.html">An overview of libxml architecture</a></li>
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<li><a href="tree.html">The tree output</a></li>
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<li><a href="interface.html">The SAX interface</a></li>
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<li><a href="library.html">The XML library interfaces</a></li>
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<li><a href="entities.html">Entities or no entities</a></li>
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<li><a href="namespaces.html">Namespaces</a></li>
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<li><a href="valid.html">Validation, or are you afraid of DTDs ?</a></li>
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<li><a href="DOM.html">DOM Principles</a></li>
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<li><a href="example.html">A real example</a></li>
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<li><a href="contribs.html">Contributions</a></li>
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<li><a href="encoding.html">Encodings support</a></li>
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<li><a href="catalog.html">Catalogs support</a></li>
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<li><a href="xmlio.html">I/O interfaces</a></li>
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<li><a href="xmlmem.html">Memory interfaces</a></li>
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<li><a href="xmldtd.html">DTD support</a></li>
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<li><a href="xml.html">flat page</a></li>
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</ul></td></tr>
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</table></td></tr></table></td>
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<td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd">
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<p>Entities in principle are similar to simple C macros. An entity defines an
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abbreviation for a given string that you can reuse many times throughout the
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content of your document. Entities are especially useful when a given string
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may occur frequently within a document, or to confine the change needed to a
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document to a restricted area in the internal subset of the document (at the
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beginning). Example:</p>
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<pre>1 <?xml version="1.0"?>
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2 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
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3 <!ENTITY xml "Extensible Markup Language">
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4 ]>
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5 <EXAMPLE>
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6 &xml;
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7 </EXAMPLE></pre>
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<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
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its name with '&' and following it by ';' without any spaces added. There
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are 5 predefined entities in libxml allowing you to escape charaters with
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predefined meaning in some parts of the xml document content:
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<strong>&lt;</strong> for the character '<', <strong>&gt;</strong>
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for the character '>', <strong>&apos;</strong> for the character ''',
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<strong>&quot;</strong> for the character '"', and
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<strong>&amp;</strong> for the character '&'.</p>
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<p>One of the problems related to entities is that you may want the parser to
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substitute an entity's content so that you can see the replacement text in
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your application. Or you may prefer to keep entity references as such in the
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content to be able to save the document back without losing this usually
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precious information (if the user went through the pain of explicitly
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defining entities, he may have a a rather negative attitude if you blindly
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susbtitute them as saving time). The <a href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
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function allows you to check and change the behaviour, which is to not
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substitute entities by default.</p>
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<p>Here is the DOM tree built by libxml for the previous document in the
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default case:</p>
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<pre>/gnome/src/gnome-xml -> ./xmllint --debug test/ent1
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DOCUMENT
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version=1.0
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ELEMENT EXAMPLE
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TEXT
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content=
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ENTITY_REF
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INTERNAL_GENERAL_ENTITY xml
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content=Extensible Markup Language
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TEXT
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content=</pre>
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<p>And here is the result when substituting entities:</p>
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<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
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DOCUMENT
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version=1.0
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ELEMENT EXAMPLE
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TEXT
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content= Extensible Markup Language</pre>
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<p>So, entities or no entities? Basically, it depends on your use case. I
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suggest that you keep the non-substituting default behaviour and avoid using
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entities in your XML document or data if you are not willing to handle the
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entity references elements in the DOM tree.</p>
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<p>Note that at save time libxml enforces the conversion of the predefined
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entities where necessary to prevent well-formedness problems, and will also
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transparently replace those with chars (i.e. it will not generate entity
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reference elements in the DOM tree or call the reference() SAX callback when
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finding them in the input).</p>
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<p>
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<span style="background-color: #FF0000">WARNING</span>: handling entities
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on top of the libxml SAX interface is difficult!!! If you plan to use
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non-predefined entities in your documents, then the learning cuvre to handle
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then using the SAX API may be long. If you plan to use complex documents, I
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strongly suggest you consider using the DOM interface instead and let libxml
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deal with the complexity rather than trying to do it yourself.</p>
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<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
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</td></tr></table></td></tr></table></td></tr></table></td>
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</tr></table></td></tr></table>
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</body>
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</html>
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