XML::Parser::Expat






XML::Parser::Expat − Lowlevel access to James Clark’s expat
XML parser


 use XML::Parser::Expat;

      $parser = new XML::Parser::Expat;
 $parser‐>setHandlers(’Start’ => \&sh,
                      ’End’   => \&eh,
                      ’Char’  => \&ch);
 open(FOO, ’info.xml’) or die "Couldn’t open";
 $parser‐>parse(*FOO);
 close(FOO);
 # $parser‐>parse(’<foo id="me"> here <em>we</em> go </foo>’);

      sub sh
 {
   my ($p, $el, %atts) = @_;
   $p‐>setHandlers(’Char’ => \&spec)
     if ($el eq ’special’);
   ...
 }

      sub eh
 {
   my ($p, $el) = @_;
   $p‐>setHandlers(’Char’ => \&ch)  # Special elements won’t contain
     if ($el eq ’special’);         # other special elements
   ...
 }

This module provides an interface to James Clark’s XML
parser, expat. As in expat, a single instance of the parser
can only parse one document. Calls to parsestring after the
first for a given instance will die.

     Expat (and XML::Parser::Expat) are event based. As the
parser recognizes parts of the document (say the start or
end of an XML element), then any handlers registered for
that type of an event are called with suitable parameters.



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

    * ProtocolEncoding
        The protocol encoding name. The default is none. The
        expat 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. Setting the
        protocol encoding overrides any encoding in the XML









                             ‐2‐


        declaration.

    * Namespaces
        When this option is given with a true value, then
        the parser does namespace processing. By default,
        namespace processing is turned off. When it is
        turned on, the parser consumes xmlns attributes and
        strips off prefixes from element and attributes
        names where those prefixes have a defined namespace.
        A name’s namespace can be found using the
        "namespace" method and two names can be checked for
        absolute equality with the "eq_name" method.

    * NoExpand
        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 option 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.

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

    * ParseParamEnt
        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.

    * Base
        The base to use for relative pathnames or URLs. This
        can also be done by using the base method.

setHandlers(TYPE, HANDLER [, TYPE, HANDLER [...]])
    This method registers handlers for the various events.
    If no handlers are registered, then a call to
    parsestring or parsefile will only determine if the
    corresponding XML document is well formed (by returning
    without error.)  This may be called from within a
    handler, after the parse has started.









                             ‐3‐


    Setting a handler to something that evaluates to false
    unsets that handler.

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

    The recognized events and the parameters passed to the
    corresponding handlers are:

    * Start             (Parser, Element [, Attr, Val
        [,...]])
        This event is generated when an XML start tag is
        recognized. Parser is an XML::Parser::Expat
        instance. Element is the name of the XML element
        that is opened with the start tag. The Attr & Val
        pairs are generated for each attribute in the start
        tag.

    * End               (Parser, 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.

        There is always a lower level start and end handler
        installed that wrap the corresponding callbacks.
        This is to handle the context mechanism.  A
        consequence of this is that the default handler (see
        below) will not see a start tag or end tag unless
        the default_current method is called.

    * Char              (Parser, 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              (Parser, Target, Data)
        This event is generated when a processing
        instruction is recognized.

    * Comment           (Parser, String)
        This event is generated when a comment is
        recognized.

    * CdataStart        (Parser)
        This is called at the start of a CDATA section.

    * CdataEnd          (Parser)
        This is called at the end of a CDATA section.









                             ‐4‐


    * Default           (Parser, 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.

    * Unparsed          (Parser, 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          (Parser, 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         (Parser, 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).

    * ExternEntFin      (Parser)
        This is called after an external entity has been
        parsed. It allows applications to perform cleanup on
        actions performed in the above ExternEnt handler.

    * Entity            (Parser, Name, Val, Sysid, Pubid,
        Ndata, IsParam)
        This is called when an entity is declared. For









                             ‐5‐


        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           (Parser, 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::ContentModel object. See
        "XML::Parser::ContentModel Methods" for methods
        available for this class.

    * Attlist           (Parser, 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.

    * Doctype           (Parser, 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 will be true or false,
        indicating whether or not the doctype declaration
        contains an internal subset.

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










                             ‐6‐


    * XMLDecl           (Parser, 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 is either undefined, or true or false.
        Undefined indicates that no standalone parameter was
        given in the XML declaration. True or false
        indicates "yes" or "no" respectively.

namespace(name)
    Return the URI of the namespace that the name belongs
    to. If the name doesn’t belong to any namespace, an
    undef is returned. This is only valid on names received
    through the Start or End handlers from a single
    document, or through a call to the generate_ns_name
    method. In other words, don’t use names generated from
    one instance of XML::Parser::Expat with other instances.

eq_name(name1, name2)
    Return true if name1 and name2 are identical (i.e. same
    name and from the same namespace.) This is only
    meaningful if both names were obtained through the Start
    or End handlers from a single document, or through a
    call to the generate_ns_name method.

generate_ns_name(name, namespace)
    Return a name, associated with a given namespace, good
    for using with the above 2 methods. The namespace
    argument should be the namespace URI, not a prefix.

new_ns_prefixes
    When called from a start tag handler, returns namespace
    prefixes declared with this start tag. If called
    elsewere (or if there were no namespace prefixes
    declared), it returns an empty list. Setting of the
    default namespace is indicated with ’#default’ as a
    prefix.

expand_ns_prefix(prefix)
    Return the uri to which the given prefix is currently
    bound. Returns undef if the prefix isn’t currently
    bound. Use ’#default’ to find the current binding of the
    default namespace (if any).

current_ns_prefixes
    Return a list of currently bound namespace prefixes. The
    order of the the prefixes in the list has no meaning. If
    the default namespace is currently bound, ’#default’
    appears in the list.

recognized_string
    Returns the string from the document that was recognized
    in order to call the current handler. For instance, when









                             ‐7‐


    called from a start handler, it will give us the the
    start‐tag string. The string is encoded in UTF−8.  This
    method doesn’t return a meaningful string inside
    declaration handlers.

original_string
    Returns the verbatim string from the document that was
    recognized in order to call the current handler. The
    string is in the original document encoding. This method
    doesn’t return a meaningful string inside declaration
    handlers.

default_current
    When called from a handler, causes the sequence of
    characters that generated the corresponding event to be
    sent to the default handler (if one is registered). Use
    of this method is deprecated in favor the
    recognized_string method, which you can use without
    installing a default handler. This method doesn’t
    deliver a meaningful string to the default handler when
    called from inside declaration handlers.

xpcroak(message)
    Concatenate onto the given message the current line
    number within the XML document plus the message implied
    by ErrorContext. Then croak with the formed message.

xpcarp(message)
    Concatenate onto the given message the current line
    number within the XML document plus the message implied
    by ErrorContext. Then carp with the formed message.

current_line
    Returns the line number of the current position of the
    parse.

current_column
    Returns the column number of the current position of the
    parse.

current_byte
    Returns the current position of the parse.

base([NEWBASE]);
    Returns the current value of the base for resolving
    relative URIs. If NEWBASE is supplied, changes the base
    to that value.

context
    Returns a list of element names that represent open
    elements, with the last one being the innermost. Inside
    start and end tag handlers, this will be the tag of the
    parent element.










                             ‐8‐


current_element
    Returns the name of the innermost currently opened
    element. Inside start or end handlers, returns the
    parent of the element associated with those tags.

in_element(NAME)
    Returns true if NAME is equal to the name of the
    innermost currently opened element. If namespace
    processing is being used and you want to check against a
    name that may be in a namespace, then use the
    generate_ns_name method to create the NAME argument.

within_element(NAME)
    Returns the number of times the given name appears in
    the context list.  If namespace processing is being used
    and you want to check against a name that may be in a
    namespace, then use the generate_ns_name method to
    create the NAME argument.

depth
    Returns the size of the context list.

element_index
    Returns an integer that is the depth‐first visit order
    of the current element. This will be zero outside of the
    root element. For example, this will return 1 when
    called from the start handler for the root element start
    tag.

skip_until(INDEX)
    INDEX is an integer that represents an element index.
    When this method is called, all handlers are suspended
    until the start tag for an element that has an index
    number equal to INDEX is seen. If a start handler has
    been set, then this is the first tag that the start
    handler will see after skip_until has been called.

position_in_context(LINES)
    Returns a string that shows the current parse position.
    LINES should be an integer >= 0 that represents the
    number of lines on either side of the current parse line
    to place into the returned string.

xml_escape(TEXT [, CHAR [, CHAR ...]])
    Returns TEXT with markup characters turned into
    character entities. Any additional characters provided
    as arguments are also turned into character references
    where found in TEXT.

parse (SOURCE)
    The SOURCE parameter should either be a string
    containing the whole XML document, or it should be an
    open IO::Handle. Only a single document may be parsed
    for a given instance of XML::Parser::Expat, so this will









                             ‐9‐


    croak if it’s been called previously for this instance.

parsestring(XML_DOC_STRING)
    Parses the given string as an XML document. Only a
    single document may be parsed for a given instance of
    XML::Parser::Expat, so this will die if either
    parsestring or parsefile has been called for this
    instance previously.

    This method is deprecated in favor of the parse method.

parsefile(FILENAME)
    Parses the XML document in the given file. Will die if
    parsestring or parsefile has been called previously for
    this instance.

is_defaulted(ATTNAME)
    NO LONGER WORKS. To find out if an attribute is
    defaulted please use the specified_attr method.

specified_attr
    When the start handler receives lists of attributes and
    values, the non‐defaulted (i.e. explicitly specified)
    attributes occur in the list first. This method returns
    the number of specified items in the list.  So if this
    number is equal to the length of the list, there were no
    defaulted values. Otherwise the number points to the
    index of the first defaulted attribute name.

finish
    Unsets all handlers (including internal ones that set
    context), but expat continues parsing to the end of the
    document or until it finds an error.  It should finish
    up a lot faster than with the handlers set.

release
    There are data structures used by XML::Parser::Expat
    that have circular references. This means that these
    structures will never be garbage collected unless these
    references are explicitly broken. Calling this method
    breaks those references (and makes the instance
    unusable.)

    Normally, higher level calls handle this for you, but if
    you are using XML::Parser::Expat directly, then it’s
    your responsibility to call it.

     XML::Parser::ContentModel Methods

     The element declaration handlers are passed objects of
this class as the content model of the element declaration.
They also represent content particles, components of a
content model.










                            ‐10‐


     When referred to as a string, these objects are
automagicly converted to a string representation of the
model (or content particle).

isempty
    This method returns true if the object is "EMPTY", false
    otherwise.

isany
    This method returns true if the object is "ANY", false
    otherwise.

ismixed
    This method returns true if the object is "(#PCDATA)" or
    "(#PCDATA⎪...)*", false otherwise.

isname
    This method returns if the object is an element name.

ischoice
    This method returns true if the object is a choice of
    content particles.

isseq
    This method returns true if the object is a sequence of
    content particles.

quant
    This method returns undef or a string representing the
    quantifier (’?’, ’*’, ’+’) associated with the model or
    particle.

children
    This method returns undef or (for mixed, choice, and
    sequence types) an array of component content particles.
    There will always be at least one component for choices
    and sequences, but for a mixed content model of pure
    PCDATA, "(#PCDATA)", then an undef is returned.

     XML::Parser::ExpatNB Methods

     The class XML::Parser::ExpatNB is a subclass of
XML::Parser::Expat used for non‐blocking access to the expat
library. It does not support the parse, parsestring, or
parsefile methods, but it does have these additional
methods:

parse_more(DATA)
    Feed expat more text to munch on.

parse_done
    Tell expat that it’s gotten the whole document.











                            ‐11‐




XML::Parser::Expat::load_encoding(ENCODING)
    Load an external encoding. ENCODING is either the name
    of an encoding or the name of a file. The basename is
    converted to lowercase and a ’.enc’ extension is
    appended unless there’s one already there. Then, unless
    it’s an absolute pathname (i.e. begins with ’/’), the
    first file by that name discovered in the @Encoding_Path
    path list is used.

    The encoding in the file is loaded and kept in the
    %Encoding_Table table. Earlier encodings of the same
    name are replaced.

    This function is automaticly called by expat when it
    encounters an encoding it doesn’t know about. Expat
    shouldn’t call this twice for the same encoding name.
    The only reason users should use this function is to
    explicitly load an encoding not contained in the
    @Encoding_Path list.

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.