Provided by: libxml-libxml-perl_2.0108+dfsg-1ubuntu0.2_amd64 
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, it 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 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 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 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
2.0108
COPYRIGHT
2001-2007, AxKit.com Ltd.
2002-2006, Christian Glahn.
2006-2009, Petr Pajas.