expat(3)

NAME

XML::Parser::Expat - Lowlevel access to James Clark's
expat XML parser

SYNOPSIS

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
  ...
}

DESCRIPTION

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.

METHODS

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 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 dec
laration, 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 parses
tring or parsefile will only determine if the corre
sponding XML document is well formed (by returning
without error.) This may be called from within a han
dler, after the parse has started.; Setting a handler to something that evaluates to false
unsets that handler.; This method returns a list of type, handler pairs cor
responding 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 han
dler installed that wrap the corresponding call
backs. 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 recog
nized. The non-markup sequence of characters is in
String. A single non-markup sequence of characters
may generate multiple calls to this handler. What
ever 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 instruc
tion is recognized.; � Comment (Parser, String)
This event is generated when a comment is recog
nized.; � CdataStart (Parser)
This is called at the start of a CDATA section.; � CdataEnd (Parser)
This is called at the end of a CDATA section.; � Default (Parser, String)
This is called for any characters that don't have
a registered handler. This includes both charac
ters that are part of markup for which no events
are generated (markup declarations) and characters
that could generate events, but for which no han
dler 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 refer
enced. 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 han
dler.; � Entity (Parser, 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 (Parser, Name, Model)
The element handler is called when an element dec
laration is found. Name is the element name, and
Model is the content model as an XML::Parser::Con
tentModel 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 multi
ple 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 pro
vided, otherwise it's undefined. Pubid is the pub
lic id of the document type, which will be unde
fined if no public id was given. Internal will be
true or false, indicating whether or not the doc
type declaration contains an internal subset.; � DoctypeFin (Parser)
This handler is called after parsing of the DOC
TYPE declaration has finished, including any
internal or external DTD declarations.; � XMLDecl (Parser, Version, Encoding, Stan
dalone)
This handler is called for XML declarations. Ver
sion 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 sin
gle document, or through a call to the gener
ate_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 names
pace 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 mean
ing. 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 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 mean
ingful 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 dec
laration 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 recog
nized_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.
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 pro
cessing is being used and you want to check against a
name that may be in a namespace, then use the gener
ate_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 posi
tion. 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 char
acter 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 con
taining 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 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 parses
tring 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 speci
fied) 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 declara tion. They also represent content particles, components of a content model.
When referred to as a string, these objects are automag icly 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 parti
cles. 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.

FUNCTIONS

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.

AUTHORS

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 documen
tation, and added some standard package features.

docs.sk

comprehensive documentation repository