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XML::LibXML::XPathContext(3)         User Contributed Perl Documentation        XML::LibXML::XPathContext(3)



NAME
       XML::LibXML::XPathContext - XPath Evaluation

SYNOPSIS
         my $xpc = XML::LibXML::XPathContext->new();
         my $xpc = XML::LibXML::XPathContext->new($node);
         $xpc->registerNs($prefix, $namespace_uri)
         $xpc->unregisterNs($prefix)
         $uri = $xpc->lookupNs($prefix)
         $xpc->registerVarLookupFunc($callback, $data)
         $data = $xpc->getVarLookupData();
         $callback = $xpc->getVarLookupFunc();
         $xpc->unregisterVarLookupFunc($name);
         $xpc->registerFunctionNS($name, $uri, $callback)
         $xpc->unregisterFunctionNS($name, $uri)
         $xpc->registerFunction($name, $callback)
         $xpc->unregisterFunction($name)
         @nodes = $xpc->findnodes($xpath)
         @nodes = $xpc->findnodes($xpath, $context_node )
         $nodelist = $xpc->findnodes($xpath, $context_node )
         $object = $xpc->find($xpath )
         $object = $xpc->find($xpath, $context_node )
         $value = $xpc->findvalue($xpath )
         $value = $xpc->findvalue($xpath, $context_node )
         $bool = $xpc->exists( $xpath_expression, $context_node );
         $xpc->setContextNode($node)
         my $node = $xpc->getContextNode;
         $xpc->setContextPosition($position)
         my $position = $xpc->getContextPosition;
         $xpc->setContextSize($size)
         my $size = $xpc->getContextSize;
         $xpc->setContextNode($node)
       The XML::LibXML::XPathContext class provides an almost complete interface to
       libxml2's XPath implementation. With XML::LibXML::XPathContext is is possible
       to evaluate XPath expressions in the context of arbitrary node, context size,
       and context position, with a user-defined namespace-prefix mapping, custom
       XPath functions written in Perl, and even a custom XPath variable resolver.

EXAMPLES
   Namespaces
       This example demonstrates "registerNs()" method. It finds all paragraph nodes in an XHTML document.

         my $xc = XML::LibXML::XPathContext->new($xhtml_doc);
         $xc->registerNs('xhtml', 'http://www.w3.org/1999/xhtml');
         my @nodes = $xc->findnodes('//xhtml:p');

   Custom XPath functions
       This example demonstrates "registerFunction()" method by defining a function filtering nodes based on
       a Perl regular expression:

         sub grep_nodes {
           my ($nodelist,$regexp) =  @_;
           my $result = XML::LibXML::NodeList->new;
           for my $node ($nodelist->get_nodelist()) {
             $result->push($node) if $node->textContent =~ $regexp;
           }
           return $result;
         };

         my $xc = XML::LibXML::XPathContext->new($node);
         $xc->registerFunction('grep_nodes', \&grep_nodes);
         my @nodes = $xc->findnodes('//section[grep_nodes(para,"\bsearch(ing|es)?\b")]');

   Variables
       This example demonstrates "registerVarLookup()" method. We use XPath variables to recycle results of
       previous evaluations:

         sub var_lookup {
           my ($varname,$ns,$data)=@_;
           return $data->{$varname};
         }

         my $areas = XML::LibXML->new->parse_file('areas.xml');
         my $empl = XML::LibXML->new->parse_file('employees.xml');

         my $xc = XML::LibXML::XPathContext->new($empl);

         my %variables = (
           A => $xc->find('/employees/employee[@salary>10000]'),
           B => $areas->find('/areas/area[district='Brooklyn']/street'),
         );

         # get names of employees from $A working in an area listed in $B
         $xc->registerVarLookupFunc(\&var_lookup, \%variables);
         my @nodes = $xc->findnodes('$A[work_area/street = $B]/name');

METHODS
       new
             my $xpc = XML::LibXML::XPathContext->new();

           Creates a new XML::LibXML::XPathContext object without a context node.

             my $xpc = XML::LibXML::XPathContext->new($node);

           Creates a new XML::LibXML::XPathContext object with the context node set to $node.

       registerNs
             $xpc->registerNs($prefix, $namespace_uri)

           Registers namespace $prefix to $namespace_uri.

       unregisterNs
             $xpc->unregisterNs($prefix)

           Unregisters namespace $prefix.

       lookupNs
             $uri = $xpc->lookupNs($prefix)

           Returns namespace URI registered with $prefix. If $prefix is not registered to any namespace URI
           returns "undef".

       registerVarLookupFunc
             $xpc->registerVarLookupFunc($callback, $data)

           Registers variable lookup function $prefix. The registered function is executed by the XPath
           engine each time an XPath variable is evaluated. It takes three arguments: $data, variable name,
           and variable ns-URI and must return one value: a number or string or any "XML::LibXML::" object
           that can be a result of findnodes: Boolean, Literal, Number, Node (e.g.  Document, Element,
           etc.), or NodeList. For convenience, simple (non-blessed) array references containing only
           XML::LibXML::Node objects can be used instead of an XML::LibXML::NodeList.

       getVarLookupData
             $data = $xpc->getVarLookupData();

           Returns the data that have been associated with a variable lookup function during a previous call
           to "registerVarLookupFunc".

       getVarLookupFunc
             $callback = $xpc->getVarLookupFunc();

           Returns the variable lookup function previously registered with "registerVarLookupFunc".

       unregisterVarLookupFunc
             $xpc->unregisterVarLookupFunc($name);

           Unregisters variable lookup function and the associated lookup data.

       registerFunctionNS
             $xpc->registerFunctionNS($name, $uri, $callback)

           Registers an extension function $name in $uri namespace. $callback must be a CODE reference. The
           arguments of the callback function are either simple scalars or "XML::LibXML::*" objects
           depending on the XPath argument types. The function is responsible for checking the argument
           number and types. Result of the callback code must be a single value of the following types: a
           simple scalar (number, string) or an arbitrary "XML::LibXML::*" object that can be a result of
           findnodes: Boolean, Literal, Number, Node (e.g.  Document, Element, etc.), or NodeList. For
           convenience, simple (non-blessed) array references containing only XML::LibXML::Node objects can
           be used instead of a XML::LibXML::NodeList.

       unregisterFunctionNS
             $xpc->unregisterFunctionNS($name, $uri)

           Unregisters extension function $name in $uri namespace. Has the same effect as passing "undef" as
           $callback to registerFunctionNS.

       registerFunction
             $xpc->registerFunction($name, $callback)

           Same as "registerFunctionNS" but without a namespace.

       unregisterFunction
             $xpc->unregisterFunction($name)

           Same as "unregisterFunctionNS" but without a namespace.

       findnodes
             @nodes = $xpc->findnodes($xpath)

             @nodes = $xpc->findnodes($xpath, $context_node )

             $nodelist = $xpc->findnodes($xpath, $context_node )

           Performs the xpath statement on the current node and returns the result as an array. In scalar
           context, returns an XML::LibXML::NodeList object. Optionally, a node may be passed as a second
           argument to set the context node for the query.

           The xpath expression can be passed either as a string or or as a XML::LibXML::XPathExpression
           object.

       find
             $object = $xpc->find($xpath )

             $object = $xpc->find($xpath, $context_node )

           Performs the xpath expression using the current node as the context of the expression, and
           returns the result depending on what type of result the XPath expression had. For example, the
           XPath "1 * 3 +          52" results in an XML::LibXML::Number object being returned. Other
           expressions might return a XML::LibXML::Boolean object, or a XML::LibXML::Literal object (a
           string). Each of those objects uses Perl's overload feature to ``do the right thing'' in
           different contexts. Optionally, a node may be passed as a second argument to set the context node
           for the query.

           The xpath expression can be passed either as a string or or as a XML::LibXML::XPathExpression
           object.

       findvalue
             $value = $xpc->findvalue($xpath )

             $value = $xpc->findvalue($xpath, $context_node )

           Is exactly equivalent to:

             $xpc->find( $xpath, $context_node )->to_literal;

           That is, it returns the literal value of the results. This enables you to ensure that you get a
           string back from your search, allowing certain shortcuts.  This could be used as the equivalent
           of <xsl:value-of select=``some_xpath''/>.  Optionally, a node may be passed in the second
           argument to set the context node for the query.

           The xpath expression can be passed either as a string or or as a XML::LibXML::XPathExpression
           object.

       exists
             $bool = $xpc->exists( $xpath_expression, $context_node );

           This method behaves like findnodes, except that it only returns a boolean value (1 if the
           expression matches a node, 0 otherwise) and may be faster than findnodes, because the XPath
           evaluation may stop early on the first match (this is true for libxml2 >= 2.6.27).

           For XPath expressions that do not return node-set, the method returns true if the returned value
           is a non-zero number or a non-empty string.

       setContextNode
             $xpc->setContextNode($node)

           Set the current context node.

       getContextNode
             my $node = $xpc->getContextNode;

           Get the current context node.

       setContextPosition
             $xpc->setContextPosition($position)

           Set the current context position. By default, this value is -1 (and evaluating XPath function
           "position()" in the initial context raises an XPath error), but can be set to any value up to
           context size. This usually only serves to cheat the XPath engine to return given position when
           "position()" XPath function is called. Setting this value to -1 restores the default behavior.

       getContextPosition
             my $position = $xpc->getContextPosition;

           Get the current context position.

       setContextSize
             $xpc->setContextSize($size)

           Set the current context size. By default, this value is -1 (and evaluating XPath function
           "last()" in the initial context raises an XPath error), but can be set to any non-negative value.
           This usually only serves to cheat the XPath engine to return the given value when "last()" XPath
           function is called. If context size is set to 0, position is automatically also set to 0. If
           context size is positive, position is automatically set to 1. Setting context size to -1 restores
           the default behavior.

       getContextSize
             my $size = $xpc->getContextSize;

           Get the current context size.

       setContextNode
             $xpc->setContextNode($node)

           Set the current context node.

BUGS AND CAVEATS
       XML::LibXML::XPathContext objects are reentrant, meaning that you can call methods of an
       XML::LibXML::XPathContext even from XPath extension functions registered with the same object or from
       a variable lookup function. On the other hand, you should rather avoid registering new extension
       functions, namespaces and a variable lookup function from within extension functions and a variable
       lookup function, unless you want to experience untested behavior.

AUTHORS
       Ilya Martynov and Petr Pajas, based on XML::LibXML and XML::LibXSLT code by Matt Sergeant and
       Christian Glahn.

HISTORICAL REMARK
       Prior to XML::LibXML 1.61 this module was distributed separately for maintenance reasons.

AUTHORS
       Matt Sergeant, Christian Glahn, Petr Pajas

VERSION
       2.0008

COPYRIGHT
       2001-2007, AxKit.com Ltd.

       2002-2006, Christian Glahn.

       2006-2009, Petr Pajas.



perl v5.16.2                                     2012-10-22                     XML::LibXML::XPathContext(3)