NAME

    XML::XPath - a set of modules for parsing and evaluating XPath
    statements

DESCRIPTION

    This module aims to comply exactly to the XPath specification at
    http://www.w3.org/TR/xpath and yet allow extensions to be added
    in the form of functions. Modules such as XSLT and XPointer may
    need to do this as they support functionality beyond XPath.

INSTALLATION

To install this module, run the following commands:

    perl Makefile.PL
    make
    make test
    make install

SYNOPSIS

    use XML::XPath;
    use XML::XPath::XMLParser;

    my $xp = XML::XPath->new(filename => 'test.xhtml');

    my $nodeset = $xp->find('/html/body/p'); # find all paragraphs

    foreach my $node ($nodeset->get_nodelist) {
        print "FOUND\n\n",
            XML::XPath::XMLParser::as_string($node),
            "\n\n";
    }

DETAILS

    There's an awful lot to all of this, so bear with it - if you
    stick it out it should be worth it. Please get a good
    understanding of XPath by reading the spec before asking me
    questions. All of the classes and parts herein are named to be
    synonimous with the names in the specification, so consult that
    if you don't understand why I'm doing something in the code.

API

    The API of XML::XPath itself is extremely simple to allow you to
    get going almost immediately. The deeper API's are more complex,
    but you shouldn't have to touch most of that.

  new()

    This constructor follows the often seen named parameter method
    call. Parameters you can use are: filename, parser, xml, ioref
    and context. The filename parameter specifies an XML file to
    parse. The xml parameter specifies a string to parse, and the
    ioref parameter specifies an ioref to parse. The context option
    allows you to specify a context node. The context node has to be
    in the format of a node as specified in the
    XML::XPath::XMLParser manpage. The 4 parameters filename, xml,
    ioref and context are mutually exclusive - you should only
    specify one (if you specify anything other than context, the
    context node is the root of your document). The parser option
    allows you to pass in an already prepared XML::Parser object, to
    save you having to create more than one in your application (if,
    for example, you're doing more than just XPath).

        my $xp = XML::XPath->new( context => $node );

    It is very much recommended that you use only 1 XPath object
    throughout the life of your application. This is because the
    object (and it's sub-objects) maintain certain bits of state
    information that will be useful (such as XPath variables) to
    later calls to find(). It's also a good idea because you'll use
    less memory this way.

  *nodeset* = find($path, [$context])

    The find function takes an XPath expression (a string) and
    returns either an XML::XPath::NodeSet object containing the
    nodes it found (or empty if no nodes matched the path), or one
    of XML::XPath::Literal (a string), XML::XPath::Number, or
    XML::XPath::Boolean. It should always return something - and you
    can use ->isa() to find out what it returned. If you need to
    check how many nodes it found you should check $nodeset->size.
    See the XML::XPath::NodeSet manpage. An optional second
    parameter of a context node allows you to use this method
    repeatedly, for example XSLT needs to do this.

  findnodes($path, [$context])

    Returns a list of nodes found by $path, optionally in context
    $context. In scalar context returns an XML::XPath::NodeSet
    object.

  findnodes_as_string($path, [$context])

    Returns the nodes found reproduced as XML. The result is not
    guaranteed to be valid XML though.

  findvalue($path, [$context])

    Returns either a `XML::XPath::Literal', a `XML::XPath::Boolean'
    or a `XML::XPath::Number' object. If the path returns a NodeSet,
    $nodeset->to_literal is called automatically for you (and thus a
    `XML::XPath::Literal' is returned). Note that for each of the
    objects stringification is overloaded, so you can just print the
    value found, or manipulate it in the ways you would a normal
    perl value (e.g. using regular expressions).

  matches($node, $path, [$context])

    Returns true if the node matches the path (optionally in context
    $context).

  set_namespace($prefix, $uri)

    Sets the namespace prefix mapping to the uri.

    Normally in XML::XPath the prefixes in XPath node tests take
    their context from the current node. This means that foo:bar
    will always match an element <foo:bar> regardless of the
    namespace that the prefix foo is mapped to (which might even
    change within the document, resulting in unexpected results). In
    order to make prefixes in XPath node tests actually map to a
    real URI, you need to enable that via a call to the
    set_namespace method of your XML::XPath object.

  clear_namespaces()

    Clears all previously set namespace mappings.

  $XML::XPath::Namespaces

    Set this to 0 if you *don't* want namespace processing to occur.
    This will make everything a little (tiny) bit faster, but you'll
    suffer for it, probably.

Node Object Model

    See the XML::XPath::Node manpage, the XML::XPath::Node::Element
    manpage, the XML::XPath::Node::Text manpage, the
    XML::XPath::Node::Comment manpage, the
    XML::XPath::Node::Attribute manpage, the
    XML::XPath::Node::Namespace manpage, and the
    XML::XPath::Node::PI manpage.

On Garbage Collection
    XPath nodes work in a special way that allows circular
    references, and yet still lets Perl's reference counting garbage
    collector to clean up the nodes after use. This should be
    totally transparent to the user, with one caveat: If you free
    your tree before letting go of a sub-tree, consider that playing
    with fire and you may get burned. What does this mean to the
    average user? Not much. Provided you don't free (or let go out
    of scope) either the tree you passed to XML::XPath->new, or if
    you didn't pass a tree, and passed a filename or IO-ref, then
    provided you don't let the XML::XPath object go out of scope
    before you let results of find() and its friends go out of
    scope, then you'll be fine. Even if you do let the tree go out
    of scope before results, you'll probably still be fine. The only
    case where you may get stung is when the last part of your
    path/query is either an ancestor or parent axis. In that case
    the worst that will happen is you'll end up with a circular
    reference that won't get cleared until interpreter destruction
    time. You can get around that by explicitly calling $node-
    >DESTROY on each of your result nodes, if you really need to do
    that.

    Mail me direct if that's not clear. Note that it's not doom and
    gloom. It's by no means perfect, but the worst that will happen
    is a long running process could leak memory. Most long running
    processes will therefore be able to explicitly be careful not to
    free the tree (or XML::XPath object) before freeing results.
    AxKit, an application that uses XML::XPath, does this and I
    didn't have to make any changes to the code - it's already
    sensible programming.

    If you *really* don't want all this to happen, then set the
    variable $XML::XPath::SafeMode, and call $xp->cleanup() on the
    XML::XPath object when you're finished, or $tree->dispose() if
    you have a tree instead.

Example
    Please see the test files in t/ for examples on how to use
    XPath.

Support/Author
    This module is copyright 2000 AxKit.com Ltd. This is free
    software, and as such comes with NO WARRANTY. No dates are used
    in this module. You may distribute this module under the terms
    of either the Gnu GPL, or the Artistic License (the same terms
    as Perl itself).

    For support, please subscribe to the Perl-XML mailing list at
    the URL http://listserv.activestate.com/mailman/listinfo/perl-
    xml

    Matt Sergeant, matt@sergeant.org

SEE ALSO
    the XML::XPath::Literal manpage, the XML::XPath::Boolean
    manpage, the XML::XPath::Number manpage, the
    XML::XPath::XMLParser manpage, the XML::XPath::NodeSet manpage,
    the XML::XPath::PerlSAX manpage, the XML::XPath::Builder
    manpage.