/
Expat.pm
1233 lines (920 loc) · 33.2 KB
/
Expat.pm
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package XML::Parser::Expat;
require 5.004;
use strict;
use vars qw($VERSION @ISA %Handler_Setters %Encoding_Table @Encoding_Path
$have_File_Spec);
use Carp;
require DynaLoader;
@ISA = qw(DynaLoader);
$VERSION = "2.40";
$have_File_Spec = $INC{'File/Spec.pm'} || do 'File/Spec.pm';
%Encoding_Table = ();
if ($have_File_Spec) {
@Encoding_Path = (grep(-d $_,
map(File::Spec->catdir($_, qw(XML Parser Encodings)),
@INC)),
File::Spec->curdir);
}
else {
@Encoding_Path = (grep(-d $_, map($_ . '/XML/Parser/Encodings', @INC)), '.');
}
bootstrap XML::Parser::Expat $VERSION;
%Handler_Setters = (
Start => \&SetStartElementHandler,
End => \&SetEndElementHandler,
Char => \&SetCharacterDataHandler,
Proc => \&SetProcessingInstructionHandler,
Comment => \&SetCommentHandler,
CdataStart => \&SetStartCdataHandler,
CdataEnd => \&SetEndCdataHandler,
Default => \&SetDefaultHandler,
Unparsed => \&SetUnparsedEntityDeclHandler,
Notation => \&SetNotationDeclHandler,
ExternEnt => \&SetExternalEntityRefHandler,
ExternEntFin => \&SetExtEntFinishHandler,
Entity => \&SetEntityDeclHandler,
Element => \&SetElementDeclHandler,
Attlist => \&SetAttListDeclHandler,
Doctype => \&SetDoctypeHandler,
DoctypeFin => \&SetEndDoctypeHandler,
XMLDecl => \&SetXMLDeclHandler
);
sub new {
my ($class, %args) = @_;
my $self = bless \%args, $_[0];
$args{_State_} = 0;
$args{Context} = [];
$args{Namespaces} ||= 0;
$args{ErrorMessage} ||= '';
if ($args{Namespaces}) {
$args{Namespace_Table} = {};
$args{Namespace_List} = [undef];
$args{Prefix_Table} = {};
$args{New_Prefixes} = [];
}
$args{_Setters} = \%Handler_Setters;
$args{Parser} = ParserCreate($self, $args{ProtocolEncoding},
$args{Namespaces});
$self;
}
sub load_encoding {
my ($file) = @_;
$file =~ s!([^/]+)$!\L$1\E!;
$file .= '.enc' unless $file =~ /\.enc$/;
unless ($file =~ m!^/!) {
foreach (@Encoding_Path) {
my $tmp = ($have_File_Spec
? File::Spec->catfile($_, $file)
: "$_/$file");
if (-e $tmp) {
$file = $tmp;
last;
}
}
}
local(*ENC);
open(ENC, $file) or croak("Couldn't open encmap $file:\n$!\n");
binmode(ENC);
my $data;
my $br = sysread(ENC, $data, -s $file);
croak("Trouble reading $file:\n$!\n")
unless defined($br);
close(ENC);
my $name = LoadEncoding($data, $br);
croak("$file isn't an encmap file")
unless defined($name);
$name;
} # End load_encoding
sub setHandlers {
my ($self, @handler_pairs) = @_;
croak("Uneven number of arguments to setHandlers method")
if (int(@handler_pairs) & 1);
my @ret;
while (@handler_pairs) {
my $type = shift @handler_pairs;
my $handler = shift @handler_pairs;
croak "Handler for $type not a Code ref"
unless (! defined($handler) or ! $handler or ref($handler) eq 'CODE');
my $hndl = $self->{_Setters}->{$type};
unless (defined($hndl)) {
my @types = sort keys %{$self->{_Setters}};
croak("Unknown Expat handler type: $type\n Valid types: @types");
}
my $old = &$hndl($self->{Parser}, $handler);
push (@ret, $type, $old);
}
return @ret;
}
sub xpcroak
{
my ($self, $message) = @_;
my $eclines = $self->{ErrorContext};
my $line = GetCurrentLineNumber($_[0]->{Parser});
$message .= " at line $line";
$message .= ":\n" . $self->position_in_context($eclines)
if defined($eclines);
croak $message;
}
sub xpcarp {
my ($self, $message) = @_;
my $eclines = $self->{ErrorContext};
my $line = GetCurrentLineNumber($_[0]->{Parser});
$message .= " at line $line";
$message .= ":\n" . $self->position_in_context($eclines)
if defined($eclines);
carp $message;
}
sub default_current {
my $self = shift;
if ($self->{_State_} == 1) {
return DefaultCurrent($self->{Parser});
}
}
sub recognized_string {
my $self = shift;
if ($self->{_State_} == 1) {
return RecognizedString($self->{Parser});
}
}
sub original_string {
my $self = shift;
if ($self->{_State_} == 1) {
return OriginalString($self->{Parser});
}
}
sub current_line {
my $self = shift;
if ($self->{_State_} == 1) {
return GetCurrentLineNumber($self->{Parser});
}
}
sub current_column {
my $self = shift;
if ($self->{_State_} == 1) {
return GetCurrentColumnNumber($self->{Parser});
}
}
sub current_byte {
my $self = shift;
if ($self->{_State_} == 1) {
return GetCurrentByteIndex($self->{Parser});
}
}
sub base {
my ($self, $newbase) = @_;
my $p = $self->{Parser};
my $oldbase = GetBase($p);
SetBase($p, $newbase) if @_ > 1;
return $oldbase;
}
sub context {
my $ctx = $_[0]->{Context};
@$ctx;
}
sub current_element {
my ($self) = @_;
@{$self->{Context}} ? $self->{Context}->[-1] : undef;
}
sub in_element {
my ($self, $element) = @_;
@{$self->{Context}} ? $self->eq_name($self->{Context}->[-1], $element)
: undef;
}
sub within_element {
my ($self, $element) = @_;
my $cnt = 0;
foreach (@{$self->{Context}}) {
$cnt++ if $self->eq_name($_, $element);
}
return $cnt;
}
sub depth {
my ($self) = @_;
int(@{$self->{Context}});
}
sub element_index {
my ($self) = @_;
if ($self->{_State_} == 1) {
return ElementIndex($self->{Parser});
}
}
################
# Namespace methods
sub namespace {
my ($self, $name) = @_;
local($^W) = 0;
$self->{Namespace_List}->[int($name)];
}
sub eq_name {
my ($self, $nm1, $nm2) = @_;
local($^W) = 0;
int($nm1) == int($nm2) and $nm1 eq $nm2;
}
sub generate_ns_name {
my ($self, $name, $namespace) = @_;
$namespace ?
GenerateNSName($name, $namespace, $self->{Namespace_Table},
$self->{Namespace_List})
: $name;
}
sub new_ns_prefixes {
my ($self) = @_;
if ($self->{Namespaces}) {
return @{$self->{New_Prefixes}};
}
return ();
}
sub expand_ns_prefix {
my ($self, $prefix) = @_;
if ($self->{Namespaces}) {
my $stack = $self->{Prefix_Table}->{$prefix};
return (defined($stack) and @$stack) ? $stack->[-1] : undef;
}
return undef;
}
sub current_ns_prefixes {
my ($self) = @_;
if ($self->{Namespaces}) {
my %set = %{$self->{Prefix_Table}};
if (exists $set{'#default'} and not defined($set{'#default'}->[-1])) {
delete $set{'#default'};
}
return keys %set;
}
return ();
}
################################################################
# Namespace declaration handlers
#
sub NamespaceStart {
my ($self, $prefix, $uri) = @_;
$prefix = '#default' unless defined $prefix;
my $stack = $self->{Prefix_Table}->{$prefix};
if (defined $stack) {
push(@$stack, $uri);
}
else {
$self->{Prefix_Table}->{$prefix} = [$uri];
}
# The New_Prefixes list gets emptied at end of startElement function
# in Expat.xs
push(@{$self->{New_Prefixes}}, $prefix);
}
sub NamespaceEnd {
my ($self, $prefix) = @_;
$prefix = '#default' unless defined $prefix;
my $stack = $self->{Prefix_Table}->{$prefix};
if (@$stack > 1) {
pop(@$stack);
}
else {
delete $self->{Prefix_Table}->{$prefix};
}
}
################
sub specified_attr {
my $self = shift;
if ($self->{_State_} == 1) {
return GetSpecifiedAttributeCount($self->{Parser});
}
}
sub finish {
my ($self) = @_;
if ($self->{_State_} == 1) {
my $parser = $self->{Parser};
UnsetAllHandlers($parser);
}
}
sub position_in_context {
my ($self, $lines) = @_;
if ($self->{_State_} == 1) {
my $parser = $self->{Parser};
my ($string, $linepos) = PositionContext($parser, $lines);
return '' unless defined($string);
my $col = GetCurrentColumnNumber($parser);
my $ptr = ('=' x ($col - 1)) . '^' . "\n";
my $ret;
my $dosplit = $linepos < length($string);
$string .= "\n" unless $string =~ /\n$/;
if ($dosplit) {
$ret = substr($string, 0, $linepos) . $ptr
. substr($string, $linepos);
} else {
$ret = $string . $ptr;
}
return $ret;
}
}
sub xml_escape {
my $self = shift;
my $text = shift;
study $text;
$text =~ s/\&/\&/g;
$text =~ s/</\</g;
foreach (@_) {
croak "xml_escape: '$_' isn't a single character" if length($_) > 1;
if ($_ eq '>') {
$text =~ s/>/\>/g;
}
elsif ($_ eq '"') {
$text =~ s/\"/\"/;
}
elsif ($_ eq "'") {
$text =~ s/\'/\'/;
}
else {
my $rep = '&#' . sprintf('x%X', ord($_)) . ';';
if (/\W/) {
my $ptrn = "\\$_";
$text =~ s/$ptrn/$rep/g;
}
else {
$text =~ s/$_/$rep/g;
}
}
}
$text;
}
sub skip_until {
my $self = shift;
if ($self->{_State_} <= 1) {
SkipUntil($self->{Parser}, $_[0]);
}
}
sub release {
my $self = shift;
ParserRelease($self->{Parser});
}
sub DESTROY {
my $self = shift;
ParserFree($self->{Parser});
}
sub parse {
my $self = shift;
my $arg = shift;
croak "Parse already in progress (Expat)" if $self->{_State_};
$self->{_State_} = 1;
my $parser = $self->{Parser};
my $ioref;
my $result = 0;
if (defined $arg) {
if (ref($arg) and UNIVERSAL::isa($arg, 'IO::Handle')) {
$ioref = $arg;
} elsif (tied($arg)) {
my $class = ref($arg);
no strict 'refs';
$ioref = $arg if defined &{"${class}::TIEHANDLE"};
}
else {
require IO::Handle;
eval {
no strict 'refs';
$ioref = *{$arg}{IO} if defined *{$arg};
};
undef $@;
}
}
if (defined($ioref)) {
my $delim = $self->{Stream_Delimiter};
my $prev_rs;
$prev_rs = ref($ioref)->input_record_separator("\n$delim\n")
if defined($delim);
$result = ParseStream($parser, $ioref, $delim);
ref($ioref)->input_record_separator($prev_rs)
if defined($delim);
} else {
$result = ParseString($parser, $arg);
}
$self->{_State_} = 2;
$result or croak $self->{ErrorMessage};
}
sub parsestring {
my $self = shift;
$self->parse(@_);
}
sub parsefile {
my $self = shift;
croak "Parser has already been used" if $self->{_State_};
local(*FILE);
open(FILE, $_[0]) or croak "Couldn't open $_[0]:\n$!";
binmode(FILE);
my $ret = $self->parse(*FILE);
close(FILE);
$ret;
}
################################################################
package #hide from PAUSE
XML::Parser::ContentModel;
use overload '""' => \&asString, 'eq' => \&thiseq;
sub EMPTY () {1}
sub ANY () {2}
sub MIXED () {3}
sub NAME () {4}
sub CHOICE () {5}
sub SEQ () {6}
sub isempty {
return $_[0]->{Type} == EMPTY;
}
sub isany {
return $_[0]->{Type} == ANY;
}
sub ismixed {
return $_[0]->{Type} == MIXED;
}
sub isname {
return $_[0]->{Type} == NAME;
}
sub name {
return $_[0]->{Tag};
}
sub ischoice {
return $_[0]->{Type} == CHOICE;
}
sub isseq {
return $_[0]->{Type} == SEQ;
}
sub quant {
return $_[0]->{Quant};
}
sub children {
my $children = $_[0]->{Children};
if (defined $children) {
return @$children;
}
return undef;
}
sub asString {
my ($self) = @_;
my $ret;
if ($self->{Type} == NAME) {
$ret = $self->{Tag};
}
elsif ($self->{Type} == EMPTY) {
return "EMPTY";
}
elsif ($self->{Type} == ANY) {
return "ANY";
}
elsif ($self->{Type} == MIXED) {
$ret = '(#PCDATA';
foreach (@{$self->{Children}}) {
$ret .= '|' . $_;
}
$ret .= ')';
}
else {
my $sep = $self->{Type} == CHOICE ? '|' : ',';
$ret = '(' . join($sep, map { $_->asString } @{$self->{Children}}) . ')';
}
$ret .= $self->{Quant} if $self->{Quant};
return $ret;
}
sub thiseq {
my $self = shift;
return $self->asString eq $_[0];
}
################################################################
package #hide from PAUSE
XML::Parser::ExpatNB;
use vars qw(@ISA);
use Carp;
@ISA = qw(XML::Parser::Expat);
sub parse {
my $self = shift;
my $class = ref($self);
croak "parse method not supported in $class";
}
sub parsestring {
my $self = shift;
my $class = ref($self);
croak "parsestring method not supported in $class";
}
sub parsefile {
my $self = shift;
my $class = ref($self);
croak "parsefile method not supported in $class";
}
sub parse_more {
my ($self, $data) = @_;
$self->{_State_} = 1;
my $ret = XML::Parser::Expat::ParsePartial($self->{Parser}, $data);
croak $self->{ErrorMessage} unless $ret;
}
sub parse_done {
my $self = shift;
my $ret = XML::Parser::Expat::ParseDone($self->{Parser});
unless ($ret) {
my $msg = $self->{ErrorMessage};
$self->release;
croak $msg;
}
$self->{_State_} = 2;
my $result = $ret;
my @result = ();
my $final = $self->{FinalHandler};
if (defined $final) {
if (wantarray) {
@result = &$final($self);
}
else {
$result = &$final($self);
}
}
$self->release;
return unless defined wantarray;
return wantarray ? @result : $result;
}
################################################################
package #hide from PAUSE
XML::Parser::Encinfo;
sub DESTROY {
my $self = shift;
XML::Parser::Expat::FreeEncoding($self);
}
1;
__END__
=head1 NAME
XML::Parser::Expat - Lowlevel access to James Clark's expat XML parser
=head1 SYNOPSIS
use XML::Parser::Expat;
$parser = XML::Parser::Expat->new;
$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
...
}
=head1 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.
=head1 METHODS
=over 4
=item new
This is a class method, the constructor for XML::Parser::Expat. Options are
passed as keyword value pairs. The recognized options are:
=over 4
=item * ProtocolEncoding
The protocol encoding name. The default is none. The expat built-in
encodings are: C<UTF-8>, C<ISO-8859-1>, C<UTF-16>, and C<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.
=item * 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 I<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 L<"namespace"> method
and two names can be checked for absolute equality with the L<"eq_name">
method.
=item * 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.
=item * 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.
=item * 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.
=item * 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.
=item * Base
The base to use for relative pathnames or URLs. This can also be done by
using the base method.
=back
=item 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.
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:
=over 4
=item * 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.
=item * 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.
=item * 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.
=item * Proc (Parser, Target, Data)
This event is generated when a processing instruction is recognized.
=item * Comment (Parser, String)
This event is generated when a comment is recognized.
=item * CdataStart (Parser)
This is called at the start of a CDATA section.
=item * CdataEnd (Parser)
This is called at the end of a CDATA section.
=item * 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.
=item * 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.
=item * 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.
=item * 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).
=item * 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.
=item * 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.
=item * 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 L<"XML::Parser::ContentModel Methods">
for methods available for this class.
=item * 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.
=item * 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.
=item * DoctypeFin (Parser)
This handler is called after parsing of the DOCTYPE declaration has finished,
including any internal or external DTD declarations.
=item * 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.
=back
=item 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.
=item 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.
=item 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.
=item 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.
=item 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).
=item 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.
=item 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 meaningful string inside declaration handlers.
=item 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.
=item 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.
=item 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.