Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / libxml2 / 594cf0b2f20c5484cb915731cba921fd941745a7 / . / doc / entities.html
blob: 64ae1fa19c505ddda0b81008ddd6895d4bed9df2 [file] [log] [blame]
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
2<html>
3<head>
4<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type">
5<style type="text/css"><!--
6TD {font-size: 10pt; font-family: Verdana,Arial,Helvetica}
7BODY {font-size: 10pt; font-family: Verdana,Arial,Helvetica; margin-top: 5pt; margin-left: 0pt; margin-right: 0pt}
8H1 {font-size: 16pt; font-family: Verdana,Arial,Helvetica}
9H2 {font-size: 14pt; font-family: Verdana,Arial,Helvetica}
10H3 {font-size: 12pt; font-family: Verdana,Arial,Helvetica}
11--></style>
12<title>Entities or no entities</title>
13</head>
14<body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000">
15<table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr>
16<td width="180">
17<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>
18</td>
19<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">
20<h1>The XML C library for Gnome</h1>
21<h2>Entities or no entities</h2>
22</td></tr></table></td></tr></table></td>
23</tr></table>
24<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>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame^]25<td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td>
26<table width="100%" border="0" cellspacing="1" cellpadding="3">
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]27<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr>
28<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt">
29<li><a href="index.html">Home</a></li>
30<li><a href="FAQ.html">FAQ</a></li>
31<li><a href="intro.html">Introduction</a></li>
32<li><a href="docs.html">Documentation</a></li>
33<li><a href="bugs.html">Reporting bugs and getting help</a></li>
34<li><a href="help.html">How to help</a></li>
35<li><a href="downloads.html">Downloads</a></li>
36<li><a href="news.html">News</a></li>
37<li><a href="XML.html">XML</a></li>
38<li><a href="XSLT.html">XSLT</a></li>
39<li><a href="architecture.html">An overview of libxml architecture</a></li>
40<li><a href="tree.html">The tree output</a></li>
41<li><a href="interface.html">The SAX interface</a></li>
42<li><a href="library.html">The XML library interfaces</a></li>
43<li><a href="entities.html">Entities or no entities</a></li>
44<li><a href="namespaces.html">Namespaces</a></li>
45<li><a href="valid.html">Validation, or are you afraid of DTDs ?</a></li>
46<li><a href="DOM.html">DOM Principles</a></li>
47<li><a href="example.html">A real example</a></li>
48<li><a href="contribs.html">Contributions</a></li>
49<li><a href="encoding.html">Encodings support</a></li>
50<li><a href="catalog.html">Catalogs support</a></li>
51<li><a href="xmlio.html">I/O interfaces</a></li>
52<li><a href="xmlmem.html">Memory interfaces</a></li>
53<li><a href="xmldtd.html">DTD support</a></li>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame^]54<li>
55<a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a>
56</li>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]57</ul></td></tr>
Daniel Veillard594cf0b2001-10-25 08:09:12 +0000[diff] [blame^]58</table>
59<table width="100%" border="0" cellspacing="1" cellpadding="3">
60<tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr>
61<tr><td bgcolor="#fffacd"><ul style="margin-left: -2pt">
62<li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li>
63<li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li>
64<li><a href="http://www.cs.unibo.it/~casarini/gdome2/">DOM gdome2</a></li>
65<li><a href="ftp://xmlsoft.org/">FTP</a></li>
66<li><a href="http://www.fh-frankfurt.de/~igor/projects/libxml/">Windows binaries</a></li>
67<li><a href="http://pages.eidosnet.co.uk/~garypen/libxml/">Solaris binaries</a></li>
68</ul></td></tr>
69</table>
70</td></tr></table></td>
Daniel Veillardc9484202001-10-24 12:35:52 +0000[diff] [blame]71<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">
72<p>Entities in principle are similar to simple C macros. An entity defines an
73abbreviation for a given string that you can reuse many times throughout the
74content of your document. Entities are especially useful when a given string
75may occur frequently within a document, or to confine the change needed to a
76document to a restricted area in the internal subset of the document (at the
77beginning). Example:</p>
78<pre>1 &lt;?xml version=&quot;1.0&quot;?&gt;
792 &lt;!DOCTYPE EXAMPLE SYSTEM &quot;example.dtd&quot; [
803 &lt;!ENTITY xml &quot;Extensible Markup Language&quot;&gt;
814 ]&gt;
825 &lt;EXAMPLE&gt;
836 &amp;xml;
847 &lt;/EXAMPLE&gt;</pre>
85<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
86its name with '&amp;' and following it by ';' without any spaces added. There
87are 5 predefined entities in libxml allowing you to escape charaters with
88predefined meaning in some parts of the xml document content:
89<strong>&amp;lt;</strong> for the character '&lt;', <strong>&amp;gt;</strong>
90for the character '&gt;', <strong>&amp;apos;</strong> for the character ''',
91<strong>&amp;quot;</strong> for the character '&quot;', and
92<strong>&amp;amp;</strong> for the character '&amp;'.</p>
93<p>One of the problems related to entities is that you may want the parser to
94substitute an entity's content so that you can see the replacement text in
95your application. Or you may prefer to keep entity references as such in the
96content to be able to save the document back without losing this usually
97precious information (if the user went through the pain of explicitly
98defining entities, he may have a a rather negative attitude if you blindly
99susbtitute them as saving time). The <a href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
100function allows you to check and change the behaviour, which is to not
101substitute entities by default.</p>
102<p>Here is the DOM tree built by libxml for the previous document in the
103default case:</p>
104<pre>/gnome/src/gnome-xml -&gt; ./xmllint --debug test/ent1
105DOCUMENT
106version=1.0
107 ELEMENT EXAMPLE
108 TEXT
109 content=
110 ENTITY_REF
111 INTERNAL_GENERAL_ENTITY xml
112 content=Extensible Markup Language
113 TEXT
114 content=</pre>
115<p>And here is the result when substituting entities:</p>
116<pre>/gnome/src/gnome-xml -&gt; ./tester --debug --noent test/ent1
117DOCUMENT
118version=1.0
119 ELEMENT EXAMPLE
120 TEXT
121 content= Extensible Markup Language</pre>
122<p>So, entities or no entities? Basically, it depends on your use case. I
123suggest that you keep the non-substituting default behaviour and avoid using
124entities in your XML document or data if you are not willing to handle the
125entity references elements in the DOM tree.</p>
126<p>Note that at save time libxml enforces the conversion of the predefined
127entities where necessary to prevent well-formedness problems, and will also
128transparently replace those with chars (i.e. it will not generate entity
129reference elements in the DOM tree or call the reference() SAX callback when
130finding them in the input).</p>
131<p>
132<span style="background-color: #FF0000">WARNING</span>: handling entities
133on top of the libxml SAX interface is difficult!!! If you plan to use
134non-predefined entities in your documents, then the learning cuvre to handle
135then using the SAX API may be long. If you plan to use complex documents, I
136strongly suggest you consider using the DOM interface instead and let libxml
137deal with the complexity rather than trying to do it yourself.</p>
138<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
139</td></tr></table></td></tr></table></td></tr></table></td>
140</tr></table></td></tr></table>
141</body>
142</html>