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</style><title>Entities or no entities</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 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><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><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"><h1>The XML C parser and toolkit of Gnome</h1><h2>Entities or no entities</h2></td></tr></table></td></tr></table></td></tr></table><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><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"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Developer Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html" style="font-weight:bold">Main Menu</a></li><li><a href="html/index.html" style="font-weight:bold">Reference Manual</a></li><li><a href="examples/index.html" style="font-weight:bold">Code 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bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Entities in principle are similar to simple C macros. An entity defines
anabbreviation for a given string that you can reuse many times throughout
thecontent of your document. Entities are especially useful when a given
stringmay occur frequently within a document, or to confine the change needed
to adocument to a restricted area in the internal subset of the document (at
thebeginning). Example:</p><pre>1 &lt;?xml version="1.0"?&gt;
2 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
3 &lt;!ENTITY xml "Extensible Markup Language"&gt;
4 ]&gt;
5 &lt;EXAMPLE&gt;
6    &amp;xml;
7 &lt;/EXAMPLE&gt;</pre><p>Line 3 declares the xml entity. Line 6 uses the xml entity, by
prefixingits name with '&amp;' and following it by ';' without any spaces
added. Thereare 5 predefined entities in libxml2 allowing you to escape
characters withpredefined meaning in some parts of the xml document
content:<strong>&amp;lt;</strong>for the character '&lt;',
<strong>&amp;gt;</strong>for the character '&gt;', 
<strong>&amp;apos;</strong>for the character
''',<strong>&amp;quot;</strong>for the character '"',
and<strong>&amp;amp;</strong>for the character '&amp;'.</p><p>One of the problems related to entities is that you may want the parser
tosubstitute an entity's content so that you can see the replacement text
inyour application. Or you may prefer to keep entity references as such in
thecontent to be able to save the document back without losing this
usuallyprecious information (if the user went through the pain of
explicitlydefining entities, he may have a a rather negative attitude if you
blindlysubstitute them as saving time). The <a href="html/libxml-parser.html#xmlSubstituteEntitiesDefault">xmlSubstituteEntitiesDefault()</a>function
allows you to check and change the behaviour, which is to notsubstitute
entities by default.</p><p>Here is the DOM tree built by libxml2 for the previous document in
thedefault case:</p><pre>/gnome/src/gnome-xml -&gt; ./xmllint --debug test/ent1
DOCUMENT
version=1.0
   ELEMENT EXAMPLE
     TEXT
     content=
     ENTITY_REF
       INTERNAL_GENERAL_ENTITY xml
       content=Extensible Markup Language
     TEXT
     content=</pre><p>And here is the result when substituting entities:</p><pre>/gnome/src/gnome-xml -&gt; ./tester --debug --noent test/ent1
DOCUMENT
version=1.0
   ELEMENT EXAMPLE
     TEXT
     content=     Extensible Markup Language</pre><p>So, entities or no entities? Basically, it depends on your use case.
Isuggest that you keep the non-substituting default behaviour and avoid
usingentities in your XML document or data if you are not willing to handle
theentity references elements in the DOM tree.</p><p>Note that at save time libxml2 enforces the conversion of the
predefinedentities where necessary to prevent well-formedness problems, and
will alsotransparently replace those with chars (i.e. it will not generate
entityreference elements in the DOM tree or call the reference() SAX callback
whenfinding them in the input).</p><p><span style="background-color: #FF0000">WARNING</span>: handling
entitieson top of the libxml2 SAX interface is difficult!!! If you plan to
usenon-predefined entities in your documents, then the learning curve to
handlethen using the SAX API may be long. If you plan to use complex
documents, Istrongly suggest you consider using the DOM interface instead and
let libxmldeal with the complexity rather than trying to do it yourself.</p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>