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<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css">TD {font-family: Verdana,Arial,Helvetica}BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}H1 {font-family: Verdana,Arial,Helvetica}H2 {font-family: Verdana,Arial,Helvetica}H3 {font-family: Verdana,Arial,Helvetica}A:link, A:visited, A:active { text-decoration: underline }</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" 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bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><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"><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 <?xml version="1.0"?>2 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [3 <!ENTITY xml "Extensible Markup Language">4 ]>5 <EXAMPLE>6 &xml;7 </EXAMPLE></pre><p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixingits name with '&' 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>&lt;</strong> for the character '<', <strong>&gt;</strong>for the character '>', <strong>&apos;</strong> for the character ''',<strong>&quot;</strong> for the character '"', and<strong>&amp;</strong> for the character '&'.</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 -> ./xmllint --debug test/ent1DOCUMENTversion=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 -> ./tester --debug --noent test/ent1DOCUMENTversion=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>⌨️ 快捷键说明
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