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a namespace URI for <em>xmlns:fnord</em>.
<p> This might be changed in the future following the W3C suggestion
<a href="http://www.w3.org/2000/xmlns/">http://www.w3.org/2000/xmlns/</a>
to associate <em>xmlns</em> with the namespace <em>http://www.w3.org/2000/xmlns</em>. 
<p> As the SAX2 standard suggests <a href="qxmlsimplereader.html">QXmlSimpleReader</a> by default has
<em>http://xml.org/sax/features/namespaces</em> set to TRUE and
<em>http://xml.org/sax/features/namespace-prefixes</em> set to FALSE.
When changing this behavior using <a href="qxmlreader.html#setFeature">QXmlSimpleReader::setFeature</a>() 
note that the combination of both features set to
FALSE is illegal.
<p> For a practical demonstration of how the two features affect the 
output of the reader run the <a href="tagreader-with-features-example.html">tagreader with features example.</a> 
<p> <a name="sax2NamespacesSummary"></a>
<h4> Summary
</h4>
<a name="2-3-1"></a><p> <a href="qxmlsimplereader.html">QXmlSimpleReader</a> implements the following behavior:
<p> <center><table cellpadding="4" cellspacing="2" border="0">
<tr bgcolor="#a2c511"> <th valign="top">(namespaces, namespace-prefixes)
<th valign="top">Namespace prefix and local part
<th valign="top">Qualified names
<th valign="top">Prefix mapping
<th valign="top">xmlns attributes
<tr bgcolor="#f0f0f0"> <td valign="top">(TRUE, FALSE) <td valign="top">Yes <td valign="top">Yes* <td valign="top">Yes <td valign="top">No
<tr bgcolor="#d0d0d0"> <td valign="top">(TRUE, TRUE) <td valign="top">Yes <td valign="top">Yes <td valign="top">Yes <td valign="top">Yes
<tr bgcolor="#f0f0f0"> <td valign="top">(FALSE, TRUE) <td valign="top">No* <td valign="top">Yes <td valign="top">No* <td valign="top">Yes
<tr bgcolor="#d0d0d0"> <td valign="top">(FALSE, FALSE) <td valign="top" colspan="4" rowspan="1"> Illegal
</table></center>
<p> For the entries marked with a "*", SAX does not require a particuliar
behavior.
<p> <a name="sax2Properties"></a>
<h3> Properties
</h3>
<a name="2-4"></a><p> Properties are a more general concept. They also have a unique name,
represented as an URI, but their value is <tt>void*</tt>. Thus nearly everything
can be used as a property value. This concept involves some danger,
though: there are no means to ensure type-safety; the user must take care
that he or she passes the correct type. Properties are useful if a reader supports
special handler classes.
<p> 
<p> The URIs used for features and properties often look like URLs, e.g. 
<a href="http://xml.org/sax/features/namespace">http://xml.org/sax/features/namespace</a>. This does not mean that whatsoever
data is required at this address. It is simply a way to define unique names.
<p> Everybody can define and use new SAX2 properties for his or her
readers. Property support is however not
required.
<p> To set or query properties the following functions are provided:
<a href="qxmlreader.html#setProperty">QXmlReader::setProperty</a>(), <a href="qxmlreader.html#property">QXmlReader::property</a>() and <a href="qxmlreader.html#hasProperty">QXmlReader::hasProperty</a>().                      
<p> <a name="sax2Reading"></a>
<h3> Further reading
</h3>
<a name="2-5"></a><p> For a practical example on how to use the Qt SAX2 classes see the 
<a href="xml-sax-walkthrough.html">tagreader walkthrough.</a>
<p> More information about XML (e.g. <a href="xml.html#namespaces">namespaces</a>)
can be found in the <a href="xml.html">introduction to the Qt XML module.</a>
<p> <a name="dom"></a>
<h2> The Qt DOM classes
</h2>
<a name="3"></a><p> <a name="domIntro"></a>
<h3> Introduction to DOM
</h3>
<a name="3-1"></a><p> DOM provides an interface to access and change the content and structure of
an XML file. It makes a hierarchical view of the document (tree) 
available with the root element of the XML file serving as its root. 
Thus -- in contrast to the SAX2 interface -- an object model of the document 
is resident in memory after parsing which makes manipulation easy. 
<p> In the Qt implementation of the DOM all
nodes in the document tree are subclasses of <a href="qdomnode.html">QDomNode</a>.
The document itself is represented as a <a href="qdomdocument.html">QDomDocument</a> object.
<p> Here are the available node classes and their potential children classes:
<p> <ul>
<li> <a href="qdomdocument.html">QDomDocument</a>: Possible children are
<ul>
<li> <a href="qdomelement.html">QDomElement</a> (at most one)
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>
<li> <a href="qdomcomment.html">QDomComment</a>
<li> <a href="qdomdocumenttype.html">QDomDocumentType</a>
</ul>
<li> <a href="qdomdocumentfragment.html">QDomDocumentFragment</a>: Possible children are
<ul>
<li> <a href="qdomelement.html">QDomElement</a>
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>
<li> <a href="qdomcomment.html">QDomComment</a>
<li> <a href="qdomtext.html">QDomText</a>
<li> <a href="qdomcdatasection.html">QDomCDATASection</a>
<li> <a href="qdomentityreference.html">QDomEntityReference</a>
</ul>
<li> <a href="qdomdocumenttype.html">QDomDocumentType</a>: No children
<li> <a href="qdomentityreference.html">QDomEntityReference</a>: Possible children are
<ul>
<li> <a href="qdomelement.html">QDomElement</a>
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>
<li> <a href="qdomcomment.html">QDomComment</a>
<li> <a href="qdomtext.html">QDomText</a>
<li> <a href="qdomcdatasection.html">QDomCDATASection</a>
<li> <a href="qdomentityreference.html">QDomEntityReference</a>
</ul>
<li> <a href="qdomelement.html">QDomElement</a>: Possible children are
<ul>
<li> <a href="qdomelement.html">QDomElement</a>
<li> <a href="qdomtext.html">QDomText</a>
<li> <a href="qdomcomment.html">QDomComment</a>
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>
<li> <a href="qdomcdatasection.html">QDomCDATASection</a>
<li> <a href="qdomentityreference.html">QDomEntityReference</a>
</ul>
<li> <a href="qdomattr.html">QDomAttr</a>: Possible children are
<ul>
<li> <a href="qdomtext.html">QDomText</a>
<li> <a href="qdomentityreference.html">QDomEntityReference</a>
</ul>
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>: No children
<li> <a href="qdomcomment.html">QDomComment</a>: No children
<li> <a href="qdomtext.html">QDomText</a>: No children
<li> <a href="qdomcdatasection.html">QDomCDATASection</a>: No children
<li> <a href="qdomentity.html">QDomEntity</a>: Possible children are
<ul>
<li> <a href="qdomelement.html">QDomElement</a>
<li> <a href="qdomprocessinginstruction.html">QDomProcessingInstruction</a>
<li> <a href="qdomcomment.html">QDomComment</a>
<li> <a href="qdomtext.html">QDomText</a>
<li> <a href="qdomcdatasection.html">QDomCDATASection</a>
<li> <a href="qdomentityreference.html">QDomEntityReference</a>
</ul>
<li> <a href="qdomnotation.html">QDomNotation</a>: No children
</ul>
<p> With <a href="qdomnodelist.html">QDomNodeList</a> and <a href="qdomnamednodemap.html">QDomNamedNodeMap</a> two <a href="collection.html#collection-classes">collection classes</a> 
are provided: <a href="qdomnodelist.html">QDomNodeList</a> is a list of nodes
whereas <a href="qdomnamednodemap.html">QDomNamedNodeMap</a> is used to handle unordered sets of nodes
(often used for attributes).
<p> The <a href="qdomimplementation.html">QDomImplementation</a> class allows the user to query features of the
DOM implementation.
<p> <h3> Further reading
</h3>
<a name="3-2"></a><p> To get started please refer to the <a href="qdomdocument.html">QDomDocument</a> documentation that
describes basic usage.
<p> <a name="namespaces"></a>
<h2> An introduction to namespaces
</h2>
<a name="4"></a><p> Parts of the Qt XML module documentation assume that you are
familiar with XML namespaces. Here we present a brief introduction;
skip to <a href="#namespacesConventions">Qt XML
documentation conventions</a> if you know this material.
<p> Namespaces are a concept introduced into XML to allow a more modular design.
With their help data processing software can easily
resolve naming conflicts in XML documents.
<p> Consider the following example:
<p> <pre>
&lt;document&gt;
&lt;book&gt;
  &lt;title&gt;Practical XML&lt;/title&gt;
  &lt;author title="Ms" name="Eris Kallisti"/&gt;
  &lt;chapter&gt;
    &lt;title&gt;A Namespace Called fnord&lt;/title&gt;
  &lt;/chapter&gt;
&lt;/book&gt;
&lt;/document&gt;
</pre>
 
<p> Here we find three different uses of the name <em>title</em>. If you wish
to process this document you will encounter problems
because each of the <em>titles</em> should be displayed in a different manner --
even though they have the same name.
<p> The solution would be to have some means of identifying the
first occurrence of <em>title</em> as the title of a book, i.e.
to use the <em>title</em> element of a
book namespace to distinguish it from for example the chapter title, e.g.:
<pre>
&lt;book:title&gt;Practical XML&lt;/book:title&gt;
</pre>
 
<p> <em>book</em> in this case is
a <em>prefix</em> denoting the namespace.
<p> Before we can apply a
namespace to element or attribute names we must declare it.
<p> Namespaces are URIs like <em>http://trolltech.com/fnord/book/</em>.
This does not mean that data must be available at this
address; the URI is simply used to provide a unique name.
<p> We declare namespaces in the same way as
attributes; strictly speaking they <em>are</em> attributes.
To make for example <em>http://trolltech.com/fnord/</em> the document's
default XML namespace <em>xmlns</em> we write
<p> <pre>
xmlns="http://trolltech.com/fnord/"
</pre>
 
<p> To distinguish the <em>http://trolltech.com/fnord/book/</em> namespace
from the default, we have to supply it with a prefix:
<p> <pre>
xmlns:book="http://trolltech.com/fnord/book/"
</pre>
 
<p> A namespace that is declared like this can be applied
to element and attribute names by prepending the appropriate
prefix and a ":" delimiter. We have already seen this with
the <em>book:title</em> element.
<p> Element names without a prefix belong to the default namespace.
This rule does not apply to attributes: an attribute
without a prefix does not belong to any of the declared
XML namespaces at all.
Attributes always belong to the "traditional" namespace
of the element in which they appear. A "traditional" namespace
is not an XML namespace, it simply means that all attribute names
belonging to one element must be different. Later we will see how
to assign an XML namespace to an attribute.
<p> Due to the fact that attributes without prefixes are not in any
XML namespace there is
no collision between the attribute <em>title</em> (that belongs to the
<em>author</em> element) and for example the <em>title</em> element within a <em>chapter</em>.
<p> Let's clarify matters with an example:
<pre>
&lt;document xmlns:book = 'http://trolltech.com/fnord/book/'
          xmlns      = 'http://trolltech.com/fnord/' &gt;
&lt;book&gt;
  &lt;book:title&gt;Practical XML&lt;/book:title&gt;
  &lt;book:author xmlns:fnord = 'http://trolltech.com/fnord/'
               title="Ms"
               fnord:title="Goddess"
               name="Eris Kallisti"/&gt;
  &lt;chapter&gt;
    &lt;title&gt;A Namespace Called fnord&lt;/title&gt;
  &lt;/chapter&gt;
&lt;/book&gt;
&lt;/document&gt;
</pre>
 
<p> Within the <em>document</em> element we have two namespaces declared.
The default namespace <em>http://trolltech.com/fnord/</em>
applies to the <em>book</em> element, the <em>chapter</em> element,
the appropriate <em>title</em> element and of course to <em>document</em> itself.
<p> The <em>book:author</em> and <em>book:title</em> elements
belong to the namespace with the
URI <em>http://trolltech.com/fnord/book/</em>.
<p> The two <em>book:author</em> attributes <em>title</em> and <em>name</em> have no XML namespace
assigned.
They are only members of the "traditional" namespace of the element
<em>book:author</em>, meaning that for example two <em>title</em> attributes
in <em>book:author</em> are forbidden.
<p> In the above example we circumvent the last rule by adding a <em>title</em>
attribute from the <em>http://trolltech.com/fnord/</em> namespace to <em>book:author</em>:
the <em>fnord:title</em> comes from the namespace with the prefix <em>fnord</em>
that is declared in the <em>book:author</em> element.
<p> Clearly the <em>fnord</em> namespace has the same namespace URI as the
default namespace. So why didn't we simply use the
default namespace we'd already declared? The answer is quite complex:
<ul>
<li> attributes without a prefix don't belong to any XML namespace at all,
even not to the default namespace;
<li> additionally omitting the prefix would lead to a <em>title-title</em> clash;
<li> writing it as <em>xmlns:title</em> would declare a new namespace with
the prefix <em>title</em> instead of applying the default <em>xmlns</em> namespace.
</ul>
<p> With the Qt XML classes elements and attributes can be accessed in two ways: either
by refering to their qualified names consisting of the namespace prefix
and the "real" name (or <em>local</em> name) or
by the combination of local name and namespace URI.
<p> More information on XML namespaces can be found at
<a href="http://www.w3.org/TR/REC-xml-names/">http://www.w3.org/TR/REC-xml-names/</a>.
<p> <a name="namespacesConventions"></a>
<h3> Conventions used in Qt XML documentation
</h3>
<a name="4-1"></a><p> The following terms are used to distinguish the parts of names within the context of
namespaces:
<ul>
<li>  The <em>qualified name</em>
is the name as it appears in the document. (In the above example <em>book:title</em> is a qualified name.)
<li>  A <em>namespace prefix</em> in a qualified name
is the part to the left of the ":".  (<em>book</em> is the namespace prefix in
<em>book:title</em>.)
<li>  The <em>local part</em> of a name (also refered to as the <em>local name</em>) appears
to the right of the ":".
(Thus <em>title</em> is the local part of <em>book:title</em>.)
<li>  The <em>namespace URI</em> ("Uniform Resource Identifier") is a unique
identifier for a namespace. It looks like a URL
(e.g. <em>http://trolltech.com/fnord/</em> ) but does not require
data to be accessible by the given protocol at the named address.
</ul>
<p> Elements without a ":" (like <em>chapter</em> in the example) do not have a
namespace prefix. In this case the local part and the qualified name
are identical (i.e. <em>chapter</em>).

<!-- eof -->
<p><address><hr><div align=center>
<table width=100% cellspacing=0 border=0><tr>
<td>Copyright &copy; 2002 
<a href="http://www.trolltech.com">Trolltech</a><td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a>
<td align=right><div align=right>Qt version 3.0.5</div>
</table></div></address></body>
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