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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
definesanabbreviation for a given string that you can reuse many times
throughoutthecontent of your document. Entities are especially useful when a
givenstringmay occur frequently within a document, or to confine the change
neededto adocument to a restricted area in the internal subset of the
document (atthebeginning). 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, byprefixingits
name with '&' and following it by ';' without any spacesadded. Thereare 5
predefined entities in libxml2 allowing you to escapecharacters
withpredefined meaning in some parts of the xml
documentcontent:<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
parsertosubstitute an entity's content so that you can see the replacement
textinyour application. Or you may prefer to keep entity references as such
inthecontent to be able to save the document back without losing
thisusuallyprecious information (if the user went through the pain
ofexplicitlydefining entities, he may have a a rather negative attitude if
youblindlysubstitute them as saving time). The <a href="html/libxml-parser.html#xmlSubstituteEntitiesDefault">xmlSubstituteEntitiesDefault()</a>functionallows
you to check and change the behaviour, which is to notsubstituteentities by
default.</p><p>Here is the DOM tree built by libxml2 for the previous document
inthedefault case:</p><pre>/gnome/src/gnome-xml -> ./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 -> ./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
avoidusingentities in your XML document or data if you are not willing to
handletheentity references elements in the DOM tree.</p><p>Note that at save time libxml2 enforces the conversion of
thepredefinedentities where necessary to prevent well-formedness problems,
andwill alsotransparently replace those with chars (i.e. it will not
generateentityreference elements in the DOM tree or call the reference() SAX
callbackwhenfinding them in the input).</p><p><span style="background-color: #FF0000">WARNING</span>: handlingentitieson
top of the libxml2 SAX interface is difficult!!! If you plan
tousenon-predefined entities in your documents, then the learning curve
tohandlethen using the SAX API may be long. If you plan to use
complexdocuments, Istrongly suggest you consider using the DOM interface
instead andlet 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>
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