XML::Parser






XML::Parser − A perl module for parsing XML documents


  use XML::Parser;

       $p1 = new XML::Parser(Style => ’Debug’);
  $p1‐>parsefile(’REC‐xml‐19980210.xml’);
  $p1‐>parse(’<foo id="me">Hello World</foo>’);

       # Alternative
  $p2 = new XML::Parser(Handlers => {Start => \&handle_start,
                                     End   => \&handle_end,
                                     Char  => \&handle_char});
  $p2‐>parse($socket);

       # Another alternative
  $p3 = new XML::Parser(ErrorContext => 2);

       $p3‐>setHandlers(Char    => \&text,
                   Default => \&other);

       open(FOO, ’xmlgenerator ⎪’);
  $p3‐>parse(*FOO, ProtocolEncoding => ’ISO‐8859‐1’);
  close(FOO);

       $p3‐>parsefile(’junk.xml’, ErrorContext => 3);

This module provides ways to parse XML documents. It is
built on top of XML::Parser::Expat, which is a lower level
interface to James Clark’s expat library. Each call to one
of the parsing methods creates a new instance of
XML::Parser::Expat which is then used to parse the document.
Expat options may be provided when the XML::Parser object is
created.  These options are then passed on to the Expat
object on each parse call.  They can also be given as extra
arguments to the parse methods, in which case they override
options given at XML::Parser creation time.

     The behavior of the parser is controlled either by
""Style"" and/or ""Handlers"" options, or by "setHandlers"
method. These all provide mechanisms for XML::Parser to set
the handlers needed by XML::Parser::Expat.  If neither
"Style" nor "Handlers" are specified, then parsing just
checks the document for being well−formed.

     When underlying handlers get called, they receive as
their first parameter the Expat object, not the Parser
object.



new This is a class method, the constructor for XML::Parser.
    Options are passed as keyword value pairs. Recognized
    options are:









                             ‐2‐


    * Style
        This option provides an easy way to create a given
        style of parser. The built in styles are: "Debug",
        "Subs", "Tree", "Objects", and "Stream". These are
        all defined in separate packages under
        "XML::Parser::Style::*", and you can find further
        documentation for each style both below, and in
        those packages.

        Custom styles can be provided by giving a full
        package name containing at least one ’::’. This
        package should then have subs defined for each
        handler it wishes to have installed. See "STYLES"
        below for a discussion of each built in style.

    * Handlers
        When provided, this option should be an anonymous
        hash containing as keys the type of handler and as
        values a sub reference to handle that type of event.
        All the handlers get passed as their 1st parameter
        the instance of expat that is parsing the document.
        Further details on handlers can be found in
        "HANDLERS". Any handler set here overrides the
        corresponding handler set with the Style option.

    * Pkg
        Some styles will refer to subs defined in this
        package. If not provided, it defaults to the package
        which called the constructor.

    * ErrorContext
        This is an Expat option. When this option is
        defined, errors are reported in context. The value
        should be the number of lines to show on either side
        of the line in which the error occurred.

    * ProtocolEncoding
        This is an Expat option. This sets the protocol
        encoding name. It defaults to none. The built‐in
        encodings are: "UTF−8", "ISO−8859−1", "UTF−16", and
        "US−ASCII". Other encodings may be used if they have
        encoding maps in one of the directories in the
        @Encoding_Path list. Check "ENCODINGS" for more
        information on encoding maps. Setting the protocol
        encoding overrides any encoding in the XML
        declaration.

    * Namespaces
        This is an Expat option. If this is set to a true
        value, then namespace processing is done during the
        parse. See "Namespaces" in XML::Parser::Expat for
        further discussion of namespace processing.











                             ‐3‐


    * NoExpand
        This is an Expat option. Normally, the parser will
        try to expand references to entities defined in the
        internal subset. If this option is set to a true
        value, and a default handler is also set, then the
        default handler will be called when an entity
        reference is seen in text. This has no effect if a
        default handler has not been registered, and it has
        no effect on the expansion of entity references
        inside attribute values.

    * Stream_Delimiter
        This is an Expat option. It takes a string value.
        When this string is found alone on a line while
        parsing from a stream, then the parse is ended as if
        it saw an end of file. The intended use is with a
        stream of xml documents in a MIME multipart format.
        The string should not contain a trailing newline.

    * ParseParamEnt
        This is an Expat option. Unless standalone is set to
        "yes" in the XML declaration, setting this to a true
        value allows the external DTD to be read, and
        parameter entities to be parsed and expanded.

    * NoLWP
        This option has no effect if the ExternEnt or
        ExternEntFin handlers are directly set. Otherwise,
        if true, it forces the use of a file based external
        entity handler.

    * Non‐Expat‐Options
        If provided, this should be an anonymous hash whose
        keys are options that shouldn’t be passed to Expat.
        This should only be of concern to those subclassing
        XML::Parser.

setHandlers(TYPE, HANDLER [, TYPE, HANDLER [...]])
    This method registers handlers for various parser
    events. It overrides any previous handlers registered
    through the Style or Handler options or through earlier
    calls to setHandlers. By providing a false or undefined
    value as the handler, the existing handler can be unset.

    This method returns a list of type, handler pairs
    corresponding to the input. The handlers returned are
    the ones that were in effect prior to the call.

    See a description of the handler types in "HANDLERS".

parse(SOURCE [, OPT => OPT_VALUE [...]])
    The SOURCE parameter should either be a string
    containing the whole XML document, or it should be an
    open IO::Handle. Constructor options to









                             ‐4‐


    XML::Parser::Expat given as keyword‐value pairs may
    follow the SOURCE parameter. These override, for this
    call, any options or attributes passed through from the
    XML::Parser instance.

    A die call is thrown if a parse error occurs. Otherwise
    it will return 1 or whatever is returned from the Final
    handler, if one is installed.  In other words, what
    parse may return depends on the style.

parsestring
    This is just an alias for parse for backwards
    compatibility.

parsefile(FILE [, OPT => OPT_VALUE [...]])
    Open FILE for reading, then call parse with the open
    handle. The file is closed no matter how parse returns.
    Returns what parse returns.

parse_start([ OPT => OPT_VALUE [...]])
    Create and return a new instance of
    XML::Parser::ExpatNB. Constructor options may be
    provided. If an init handler has been provided, it is
    called before returning the ExpatNB object. Documents
    are parsed by making incremental calls to the parse_more
    method of this object, which takes a string. A single
    call to the parse_done method of this object, which
    takes no arguments, indicates that the document is
    finished.

    If there is a final handler installed, it is executed by
    the parse_done method before returning and the
    parse_done method returns whatever is returned by the
    final handler.

Expat is an event based parser. As the parser recognizes
parts of the document (say the start or end tag for an XML
element), then any handlers registered for that type of an
event are called with suitable parameters.  All handlers
receive an instance of XML::Parser::Expat as their first
argument. See "METHODS" in XML::Parser::Expat for a
discussion of the methods that can be called on this object.

     Init                (Expat)

     This is called just before the parsing of the document
starts.

     Final                (Expat)

     This is called just after parsing has finished, but
only if no errors occurred during the parse. Parse returns
what this returns.










                             ‐5‐


     Start                (Expat, Element [, Attr, Val
[,...]])

     This event is generated when an XML start tag is
recognized. Element is the name of the XML element type that
is opened with the start tag. The Attr & Val pairs are
generated for each attribute in the start tag.

     End                (Expat, Element)

     This event is generated when an XML end tag is
recognized. Note that an XML empty tag (<foo/>) generates
both a start and an end event.

     Char                (Expat, String)

     This event is generated when non‐markup is recognized.
The non‐markup sequence of characters is in String. A single
non‐markup sequence of characters may generate multiple
calls to this handler. Whatever the encoding of the string
in the original document, this is given to the handler in
UTF−8.

     Proc                (Expat, Target, Data)

     This event is generated when a processing instruction
is recognized.

     Comment                (Expat, Data)

     This event is generated when a comment is recognized.

     CdataStart        (Expat)

     This is called at the start of a CDATA section.

     CdataEnd                (Expat)

     This is called at the end of a CDATA section.

     Default                (Expat, String)

     This is called for any characters that don’t have a
registered handler.  This includes both characters that are
part of markup for which no events are generated (markup
declarations) and characters that could generate events, but
for which no handler has been registered.

     Whatever the encoding in the original document, the
string is returned to the handler in UTF−8.













                             ‐6‐


     Unparsed                (Expat, Entity, Base, Sysid,
Pubid, Notation)

     This is called for a declaration of an unparsed entity.
Entity is the name of the entity. Base is the base to be
used for resolving a relative URI.  Sysid is the system id.
Pubid is the public id. Notation is the notation name. Base
and Pubid may be undefined.

     Notation                (Expat, Notation, Base, Sysid,
Pubid)

     This is called for a declaration of notation. Notation
is the notation name.  Base is the base to be used for
resolving a relative URI. Sysid is the system id. Pubid is
the public id. Base, Sysid, and Pubid may all be undefined.

     ExternEnt        (Expat, Base, Sysid, Pubid)

     This is called when an external entity is referenced.
Base is the base to be used for resolving a relative URI.
Sysid is the system id. Pubid is the public id. Base, and
Pubid may be undefined.

     This handler should either return a string, which
represents the contents of the external entity, or return an
open filehandle that can be read to obtain the contents of
the external entity, or return undef, which indicates the
external entity couldn’t be found and will generate a parse
error.

     If an open filehandle is returned, it must be returned
as either a glob (*FOO) or as a reference to a glob (e.g. an
instance of IO::Handle).

     A default handler is installed for this event. The
default handler is XML::Parser::lwp_ext_ent_handler unless
the NoLWP option was provided with a true value, otherwise
XML::Parser::file_ext_ent_handler is the default handler for
external entities. Even without the NoLWP option, if the URI
or LWP modules are missing, the file based handler ends up
being used after giving a warning on the first external
entity reference.

     The LWP external entity handler will use proxies
defined in the environment (http_proxy, ftp_proxy, etc.).

     Please note that the LWP external entity handler reads
the entire entity into a string and returns it, where as the
file handler opens a filehandle.

     Also note that the file external entity handler will
likely choke on absolute URIs or file names that don’t fit
the conventions of the local operating system.









                             ‐7‐


     The expat base method can be used to set a basename for
relative pathnames. If no basename is given, or if the
basename is itself a relative name, then it is relative to
the current working directory.

     ExternEntFin        (Expat)

     This is called after parsing an external entity. It’s
not called unless an ExternEnt handler is also set. There is
a default handler installed that pairs with the default
ExternEnt handler.

     If you’re going to install your own ExternEnt handler,
then you should set (or unset) this handler too.

     Entity                (Expat, Name, Val, Sysid, Pubid,
Ndata, IsParam)

     This is called when an entity is declared. For internal
entities, the Val parameter will contain the value and the
remaining three parameters will be undefined. For external
entities, the Val parameter will be undefined, the Sysid
parameter will have the system id, the Pubid parameter will
have the public id if it was provided (it will be undefined
otherwise), the Ndata parameter will contain the notation
for unparsed entities. If this is a parameter entity
declaration, then the IsParam parameter is true.

     Note that this handler and the Unparsed handler above
overlap. If both are set, then this handler will not be
called for unparsed entities.

     Element                (Expat, Name, Model)

     The element handler is called when an element
declaration is found. Name is the element name, and Model is
the content model as an XML::Parser::Content object. See
"XML::Parser::ContentModel Methods" in XML::Parser::Expat
for methods available for this class.

     Attlist                (Expat, Elname, Attname, Type,
Default, Fixed)

     This handler is called for each attribute in an ATTLIST
declaration.  So an ATTLIST declaration that has multiple
attributes will generate multiple calls to this handler. The
Elname parameter is the name of the element with which the
attribute is being associated. The Attname parameter is the
name of the attribute. Type is the attribute type, given as
a string. Default is the default value, which will either be
"#REQUIRED", "#IMPLIED" or a quoted string (i.e. the
returned string will begin and end with a quote character).
If Fixed is true, then this is a fixed attribute.










                             ‐8‐


     Doctype                (Expat, Name, Sysid, Pubid,
Internal)

     This handler is called for DOCTYPE declarations. Name
is the document type name. Sysid is the system id of the
document type, if it was provided, otherwise it’s undefined.
Pubid is the public id of the document type, which will be
undefined if no public id was given. Internal is the
internal subset, given as a string. If there was no internal
subset, it will be undefined. Internal will contain all
whitespace, comments, processing instructions, and
declarations seen in the internal subset. The declarations
will be there whether or not they have been processed by
another handler (except for unparsed entities processed by
the Unparsed handler). However, comments and processing
instructions will not appear if they’ve been processed by
their respective handlers.

     * DoctypeFin                (Parser)

     This handler is called after parsing of the DOCTYPE
declaration has finished, including any internal or external
DTD declarations.

     XMLDecl                (Expat, Version, Encoding,
Standalone)

     This handler is called for xml declarations. Version is
a string containg the version. Encoding is either undefined
or contains an encoding string.  Standalone will be either
true, false, or undefined if the standalone attribute is
yes, no, or not made respectively.



     Debug

     This just prints out the document in outline form.
Nothing special is returned by parse.

     Subs

     Each time an element starts, a sub by that name in the
package specified by the Pkg option is called with the same
parameters that the Start handler gets called with.

     Each time an element ends, a sub with that name
appended with an underscore ("_"), is called with the same
parameters that the End handler gets called with.

     Nothing special is returned by parse.












                             ‐9‐


     Tree

     Parse will return a parse tree for the document. Each
node in the tree takes the form of a tag, content pair. Text
nodes are represented with a pseudo‐tag of "0" and the
string that is their content. For elements, the content is
an array reference. The first item in the array is a
(possibly empty) hash reference containing attributes. The
remainder of the array is a sequence of tag‐content pairs
representing the content of the element.

     So for example the result of parsing:

       <foo><head id="a">Hello <em>there</em></head><bar>Howdy<ref/></bar>do</foo>

     would be:

                  Tag   Content
  ==================================================================
  [foo, [{}, head, [{id => "a"}, 0, "Hello ",  em, [{}, 0, "there"]],
              bar, [         {}, 0, "Howdy",  ref, [{}]],
                0, "do"
        ]
  ]

     The root document "foo", has 3 children: a "head"
element, a "bar" element and the text "do". After the empty
attribute hash, these are represented in it’s contents by 3
tag‐content pairs.

     Objects

     This is similar to the Tree style, except that a hash
object is created for each element. The corresponding object
will be in the class whose name is created by appending "::"
and the element name to the package set with the Pkg option.
Non‐markup text will be in the ::Characters class. The
contents of the corresponding object will be in an anonymous
array that is the value of the Kids property for that
object.

     Stream

     This style also uses the Pkg package. If none of the
subs that this style looks for is there, then the effect of
parsing with this style is to print a canonical copy of the
document without comments or declarations.  All the subs
receive as their 1st parameter the Expat instance for the
document they’re parsing.

     It looks for the following routines:

* StartDocument
    Called at the start of the parse .









                            ‐10‐


* StartTag
    Called for every start tag with a second parameter of
    the element type. The $_ variable will contain a copy of
    the tag and the %_ variable will contain attribute
    values supplied for that element.

* EndTag
    Called for every end tag with a second parameter of the
    element type. The $_ variable will contain a copy of the
    end tag.

* Text
    Called just before start or end tags with accumulated
    non‐markup text in the $_ variable.

* PI
    Called for processing instructions. The $_ variable will
    contain a copy of the PI and the target and data are
    sent as 2nd and 3rd parameters respectively.

* EndDocument
    Called at conclusion of the parse.

XML documents may be encoded in character sets other than
Unicode as long as they may be mapped into the Unicode
character set. Expat has further restrictions on encodings.
Read the xmlparse.h header file in the expat distribution to
see details on these restrictions.

     Expat has built‐in encodings for: "UTF−8",
"ISO−8859−1", "UTF−16", and "US−ASCII". Encodings are set
either through the XML declaration encoding attribute or
through the ProtocolEncoding option to XML::Parser or
XML::Parser::Expat.

     For encodings other than the built−ins, expat calls the
function load_encoding in the Expat package with the
encoding name. This function looks for a file in the path
list @XML::Parser::Expat::Encoding_Path, that matches the
lower‐cased name with a ’.enc’ extension. The first one it
finds, it loads.

     If you wish to build your own encoding maps, check out
the XML::Encoding module from CPAN.

Larry Wall <larry@wall.org> wrote version 1.0.

     Clark Cooper <coopercc@netheaven.com> picked up
support, changed the API for this version (2.x), provided
documentation, and added some standard package features.

     Matt Sergeant <matt@sergeant.org> is now maintaining
XML::Parser