Provided by: tclxml_3.3~svn11-3_amd64 
NAME
TclXML - XML parser support for Tcl
SYNOPSIS
package require xml
package require parserclass
::xml::parserclass option ? arg arg ... ?
::xml::parser ? name? ? -option value ... ?
parser option arg
DESCRIPTION
TclXML provides event-based parsing of XML documents. The application may register
callback scripts for certain document features, and when the parser encounters those
features while parsing the document the callback is evaluated.
The parser may also perform other functions, such as normalisation, validation and/or
entity expansion. Generally, these functions are under the control of configuration
options. Whether these functions can be performed at all depends on the parser
implementation.
The TclXML package provides a generic interface for use by a Tcl application, along with a
low-level interface for use by a parser implementation. Each implementation provides a
class of XML parser, and these register themselves using the ::xml::parserclass create
command. One of the registered parser classes will be the default parser class.
Loading the package with the generic package require xml command allows the package to
automatically determine the default parser class. In order to select a particular parser
class as the default, that class' package may be loaded directly, eg. package require
xml::libxml2. In all cases, all available parser classes are registered with the TclXML
package, the difference is simply in which one becomes the default.
COMMANDS
::xml::parserclass
The ::xml::parserclass command is used to manage XML parser classes.
Command Options
The following command options may be used:
create
create name ? -createcommand script? ? -createentityparsercommand script? ?
-parsecommand script? ? -configurecommand script? ? -getcommand script? ?
-deletecommand script?
Creates an XML parser class with the given name.
destroy
destroy name
Destroys an XML parser class.
info
info names default
Returns information about registered XML parser classes.
::xml::parser
The ::xml::parser command creates an XML parser object. The return value of the command
is the name of the newly created parser.
The parser scans an XML document's syntactical structure, evaluating callback scripts for
each feature found. At the very least the parser will normalise the document and check
the document for well-formedness. If the document is not well-formed then the
-errorcommand option will be evaluated. Some parser classes may perform additional
functions, such as validation. Additional features provided by the various parser classes
are described in the section Parser Classes
Parsing is performed synchronously. The command blocks until the entire document has been
parsed. Parsing may be terminated by an application callback, see the section Callback
Return Codes. Incremental parsing is also supported by using the -final configuration
option.
Configuration Options
The ::xml::parser command accepts the following configuration options:
-attlistdeclcommand
-attlistdeclcommand script
Specifies the prefix of a Tcl command to be evaluated whenever an attribute list
declaration is encountered in the DTD subset of an XML document. The command
evaluated is: script name attrname type default value
where:
name
Element type name
attrname
Attribute name being declared
type
Attribute type
default
Attribute default, such as #IMPLIED
value
Default attribute value. Empty string if none
given.
-baseuri -baseurl
-baseuri URI
-baseurl URI
Specifies the base URI for resolving relative URIs that may be used in the XML
document to refer to external entities.
-baseurl is deprecated in favour of -baseuri.
-characterdatacommand
-characterdatacommand script
Specifies the prefix of a Tcl command to be evaluated whenever character data is
encountered in the XML document being parsed. The command evaluated is: script
data
where:
data
Character data in the document
-commentcommand
-commentcommand script
Specifies the prefix of a Tcl command to be evaluated whenever a comment is
encountered in the XML document being parsed. The command evaluated is: script
data
where:
data
Comment data
-defaultcommand
-defaultcommand script
Specifies the prefix of a Tcl command to be evaluated when no other callback has
been defined for a document feature which has been encountered. The command
evaluated is: script data
where:
data
Document data
-defaultexpandinternalentities
-defaultexpandinternalentities boolean
Specifies whether entities declared in the internal DTD subset are expanded with
their replacement text. If entities are not expanded then the entity references
will be reported with no expansion.
-doctypecommand
-doctypecommand script
Specifies the prefix of a Tcl command to be evaluated when the document type
declaration is encountered. The command evaluated is: script name public system
dtd
where:
name
The name of the document element
public
Public identifier for the external DTD subset
system
System identifier for the external DTD subset.
Usually a URI.
dtd
The internal DTD subset
See also -startdoctypedeclcommand and -enddoctypedeclcommand.
-elementdeclcommand
-elementdeclcommand script
Specifies the prefix of a Tcl command to be evaluated when an element markup
declaration is encountered. The command evaluated is: script name model
where:
name
The element type name
model
Content model specification
-elementendcommand
-elementendcommand script
Specifies the prefix of a Tcl command to be evaluated when an element end tag is
encountered. The command evaluated is: script name args
where:
name
The element type name that has ended
args
Additional information about this element
Additional information about the element takes the form of configuration options.
Possible options are:
-empty
boolean
The empty element syntax was used for this element
-namespace
uri
The element is in the XML namespace associated
with the given URI
-elementstartcommand
-elementstartcommand script
Specifies the prefix of a Tcl command to be evaluated when an element start tag is
encountered. The command evaluated is: script name attlist args
where:
name
The element type name that has started
attlist
A Tcl list containing the attributes for this
element. The list of attributes is formatted as pairs of attribute
names and their values.
args
Additional information about this element
Additional information about the element takes the form of configuration options.
Possible options are:
-empty
boolean
The empty element syntax was used for this element
-namespace
uri
The element is in the XML namespace associated
with the given URI
-namespacedecls
list
The start tag included one or more XML Namespace
declarations. list is a Tcl list giving the namespaces declared.
The list is formatted as pairs of values, the first value is the
namespace URI and the second value is the prefix used for the
namespace in this document. A default XML namespace declaration will
have an empty string for the prefix.
-encoding
-encoding value
Gives the character encoding of the document. This option only has an effect
before a document is parsed. The default character encoding is utf-8. If the
value unknown is given, or any value other than utf-8, then the document text is
treated as binary data. If the value is given as unknown then the parser will
attempt to automatically determine the character encoding of the document (using
byte-order-marks, etc). If any value other than utf-8 or unknown is given then the
parser will read the document text using that character encoding.
-endcdatasectioncommand
-endcdatasectioncommand script
Specifies the prefix of a Tcl command to be evaluated when end of a CDATA section
is encountered. The command is evaluated with no further arguments.
-enddoctypedeclcommand
-enddoctypedeclcommand script
Specifies the prefix of a Tcl command to be evaluated when end of the document type
declaration is encountered. The command is evaluated with no further arguments.
-entitydeclcommand
-entitydeclcommand script
Specifies the prefix of a Tcl command to be evaluated when an entity declaration is
encountered. The command evaluated is: script name args
where:
name
The name of the entity being declared
args
Additional information about the entity
declaration. An internal entity shall have a single argument, the
replacement text. An external parsed entity shall have two
additional arguments, the public and system indentifiers of the
external resource. An external unparsed entity shall have three
additional arguments, the public and system identifiers followed by
the notation name.
-entityreferencecommand
-entityreferencecommand script
Specifies the prefix of a Tcl command to be evaluated when an entity reference is
encountered. The command evaluated is: script name
where:
name
The name of the entity being referenced
-errorcommand
-errorcommand script
Specifies the prefix of a Tcl command to be evaluated when a fatal error is
detected. The error may be due to the XML document not being well-formed. In the
case of a validating parser class, the error may also be due to the XML document
not obeying validity constraints. By default, a callback script is provided which
causes an error return code, but an application may supply a script which attempts
to continue parsing. The command evaluated is: script errorcode errormsg
where:
errorcode
A single word description of the error, intended
for use by an application
errormsg
A human-readable description of the error
-externalentitycommand
-externalentitycommand script
Specifies the prefix of a Tcl command to be evaluated to resolve an external entity
reference. If the parser has been configured to validate the XML document, a
default script is supplied that resolves the URI given as the system identifier of
the external entity and recursively parses the entity's data. If the parser has
been configured as a non-validating parser, then by default external entities are
not resolved. This option can be used to override the default behaviour. The
command evaluated is: script name baseuri uri id
where:
name
The Tcl command name of the current parser
baseuri
An absolute URI for the current entity which is to
be used to resolve relative URIs
uri
The system identifier of the external entity,
usually a URI
id
The public identifier of the external entity. If
no public identifier was given in the entity declaration then id will
be an empty string.
The return result of the callback script determines the action of the parser. Note
that these codes are interpreted in a different manner to other callbacks.
TCL_OK
The return result of the callback script is used as the external entity's
data. The URI passed to the callback script is used as the entity's base
URI.
This is useful to either override the normal loading of an entity's data, or
to implement new or alternative URI schemes. As an example, the script
below sets an external entity handler that intercepts "tcl:" URIs and
evaluates them as inline Tcl scripts:
package require xml
proc External {name baseuri uri id} {
switch -glob -- $uri { tcl:* { regexp {^tcl:(.*)$} $uri
discard script return [uplevel #0 $script] } default {
return -code continue {} }
} }
set parser [xml::parser -externalentitycommand External] $parser parse
{<!DOCTYPE example [
<!ENTITY example SYSTEM "tcl:set%20example%20HelloWorld"> ]> <example>
&example; </example> }
puts $example
This script will print "HelloWorld" to stdout.
TCL_CONTINUE
In a normal (non-safe) interpreter, the default external entity handler is
used to load the external entity data as per normal operation of the parser.
If the parser is executing in a Safe Tcl interpreter then the entity is not
loaded at all.
This is useful to interpose on the loading of external entities without
interfering with the loading of entities.
TCL_BREAK
No data is returned for this entity, ie. the entity is ignored. No error is
propagated.
TCL_ERROR
No data is returned for this entity, ie. the entity is ignored. A
background error is registered, using the result of the callback script.
-final
-final boolean
Specifies whether the XML document being parsed is complete. If the document is to
be incrementally parsed then this option will be set to false, and when the last
fragment of document is parsed it is set to true. For example,
set parser [::xml::parser -final 0] $parser parse $data1 $parser parse $data2
$parser configure -final 1 $parser parse $finaldata
-ignorewhitespace
-ignorewhitespace boolean
If this option is set to true then spans of character data in the XML document
which are composed only of white-space (CR, LF, space, tab) will not be reported to
the application. In other words, the data passed to every invocation of the
-characterdatacommand script will contain at least one non-white-space character.
-notationdeclcommand
-notationdeclcommand script
Specifies the prefix of a Tcl command to be evaluated when a notation declaration
is encountered. The command evaluated is: script name uri
where:
name
The name of the notation
uri
An external identifier for the notation, usually a
URI.
-notstandalonecommand
-notstandalonecommand script
Specifies the prefix of a Tcl command to be evaluated when the parser determines
that the XML document being parsed is not a standalone document.
-paramentityparsing
-paramentityparsing boolean
Controls whether external parameter entities are parsed.
-parameterentitydeclcommand
-parameterentitydeclcommand script
Specifies the prefix of a Tcl command to be evaluated when a parameter entity
declaration is encountered. The command evaluated is: script name args
where:
name
The name of the parameter entity
args
For an internal parameter entity there is only one
additional argument, the replacement text. For external parameter
entities there are two additional arguments, the system and public
identifiers respectively.
-parser
-parser name
The name of the parser class to instantiate for this parser object. This option
may only be specified when the parser instance is created.
-processinginstructioncommand
-processinginstructioncommand script
Specifies the prefix of a Tcl command to be evaluated when a processing instruction
is encountered. The command evaluated is: script target data
where:
target
The name of the processing instruction target
data
Remaining data from the processing instruction
-reportempty
-reportempty boolean
If this option is enabled then when an element is encountered that uses the special
empty element syntax, additional arguments are appended to the
-elementstartcommand and -elementendcommand callbacks. The arguments -empty 1
are appended. For example: script -empty 1
-startcdatasectioncommand
-startcdatasectioncommand script
Specifies the prefix of a Tcl command to be evaluated when the start of a CDATA
section section is encountered. No arguments are appended to the script.
-startdoctypedeclcommand
-startdoctypedeclcommand script
Specifies the prefix of a Tcl command to be evaluated at the start of a document
type declaration. No arguments are appended to the script.
-unknownencodingcommand
-unknownencodingcommand script
Specifies the prefix of a Tcl command to be evaluated when a character is
encountered with an unknown encoding. This option has not been implemented.
-unparsedentitydeclcommand
-unparsedentitydeclcommand script
Specifies the prefix of a Tcl command to be evaluated when a declaration is
encountered for an unparsed entity. The command evaluated is: script system public
notation
where:
system
The system identifier of the external entity,
usually a URI
public
The public identifier of the external entity
notation
The name of the notation for the external entity
-validate
-validate boolean
Enables validation of the XML document to be parsed. Any changes to this option
are ignored after an XML document has started to be parsed, but the option may be
changed after a reset.
-warningcommand
-warningcommand script
Specifies the prefix of a Tcl command to be evaluated when a warning condition is
detected. A warning condition is where the XML document has not been authored
correctly, but is still well-formed and may be valid. For example, the special
empty element syntax may be used for an element which has not been declared to have
empty content. By default, a callback script is provided which silently ignores
the warning. The command evaluated is: script warningcode warningmsg
where:
warningcode
A single word description of the warning, intended
for use by an application
wanringmsg
A human-readable description of the warning
-xmldeclcommand
-xmldeclcommand script
Specifies the prefix of a Tcl command to be evaluated when the XML declaration is
encountered. The command evaluated is: script version encoding standalone
where:
version
The version number of the XML specification to
which this document purports to conform
encoding
The character encoding of the document
standalone
A boolean declaring whether the document is
standalone
Parser Command
The ::xml::parser command creates a new Tcl command with the same name as the parser.
This command may be used to invoke various operations on the parser object. It has the
following general form: name option arg
option and the arg determine the exact behaviour of the command. The following commands
are possible for parser objects:
cget
cget -option
Returns the current value of the configuration option given by option. Option
may have any of the values accepted by the parser object.
configure
configure -option value
Modify the configuration options of the parser object. Option may have any of the
values accepted by the parser object.
entityparser
entityparser option value
Creates a new parser object. The new object inherits the same configuration
options as the parent parser object, but is able to parse XML data in a parsed
entity. The option -dtdsubset allows markup declarations to be treated as being
in the internal or external DTD subset.
free
free name
Frees all resources associated with the parser object. The object is not usable
after this command has been invoked.
get
get name args
Returns information about the XML document being parsed. Each parser class
provides different information, see the documentation for the parser class.
parse
parse xml args
Parses the XML document. The usual desired effect is for various application
callbacks to be evaluated. Other functions will also be performed by the parser
class, at the very least this includes checking the XML document for well-
formedness.
reset
reset
Initialises the parser object in preparation for parsing a new XML document.
CALLBACK RETURN CODES
Every callback script evaluated by a parser may return a return code other than TCL_OK.
Return codes are interpreted as follows:
break Suppresses invocation of all further callback scripts. The parse method
returns the TCL_OK return code.
continue Suppresses invocation of further callback scripts until the current
element has finished.
error Suppresses invocation of all further callback scripts. The parse method also
returns the TCL_ERROR return code.
default Any other return code suppresses invocation of all further callback
scripts. The parse method returns the same return code.
ERROR MESSAGES
If an error or warning condition is detected then an error message is returned. These
messages are structured as a Tcl list, as described below:
{domain level code node line message int1 int2 string1 string2 string3}
domain
A code for the subsystem that detected the error.
level
Severity level of the problem.
code
A one word string describing the error.
node
If available, the token of the DOM node associated with the problem.
line
If known, the line number in the source XML document where the problem was
detected.
message
A human-readable description of the problem.
int1
Additional integer data. For the parser domain, this is usually the column number
where the problem was detected.
int2
Additional integer data.
string1
Additional string data.
string2
Additional string data.
string3
Additional string data.
APPLICATION EXAMPLES
This script outputs the character data of an XML document read from stdin.
package require xml
proc cdata {data args} {
puts -nonewline $data }
set parser [::xml::parser -characterdatacommand cdata] $parser parse [read stdin]
This script counts the number of elements in an XML document read from stdin.
package require xml
proc EStart {varName name attlist args} {
upvar #0 $varName var
incr var }
set count 0 set parser [::xml::parser -elementstartcommand [list EStart count]] $parser
parse [read stdin] puts "The XML document contains $count elements"
SAFE XML
TclXML/Tcl and TclXML/libxml2 may be used in a Safe Tcl interpreter. When a document is
parsed in a Safe Tcl interpreter, any attempt by the XML document to load an external
entity is handled by the -externalentitycommand callback. This callback is evaluated in
the context of the safe interpreter and therefore is subject to the security policy in
force for that interpreter. The default entity loader will not be invoked, even if the
callback script returns a TCL_CONTINUE code.
See the description of the -externalentitycommand for further details.
PARSER CLASSES
This section will discuss how a parser class is implemented.
Tcl Parser Class
The pure-Tcl parser class requires no compilation - it is a collection of Tcl scripts.
This parser implementation is non-validating, ie. it can only check well-formedness in a
document. However, by enabling the -validate option it will read the document's DTD and
resolve external entities. This parser class is referred to as TclXML/tcl.
This parser implementation aims to implement XML v1.0 and supports XML Namespaces.
Generally the parser produces XML Infoset information items. That is, it gives the
application a slightly higher-level view than the raw XML syntax. For example, it does
not report CDATA Sections.
TclXML/tcl is not able to handle character encodings other than UTF-8.
libxml2 Parser Class
The libxml2 parser class provides a Tcl interface to the libxml2 XML parser library. This
parser class is referred to as TclXML/libxml2.
When the package is loaded the variable ::xml::libxml2::libxml2version is set to the
version number of the libxml2 library being used.
On MS Windows, it is necessary to load the generic XML package first, and then the
TclXML/libxml2 package. For example,
package require xml package require xml::libxml2
get Method
TclXML/libxml2 provides the following arguments to the get method:
document
Returns the parsed document object. libxml2 builds an in-memory data structure of
the XML document it parses (a DOM tree). This method returns a handle (or token)
for that structure.
TclXML/libxml2 manages the document object as a Tcl object. See the -keep for
further information.
Additional Options
-keep
-keep normal | implicit
Controls how the TclXML/libxml2 packages manages the document object. The default
value is implicit; the document is destroyed when the Tcl Object's internal
representation is freed. If the option is given the value normal then the document
must be explicit destroyed. The only way to explicitly destroy the document is by
using the C API.
-retainpath
-retainpath xpath
The given XPath location path specifies which part of the document is to be kept
after the parsing operation has completed. By default, all document data is
discard after it has been parsed.
-retainpathns
-retainpathns prefix ns ...
The value of this option is a list of pairs of XML Namespace prefixes and their
corresponding namespace URIs. These are used by the XPath location path given in
the -retainpath option.
Limitations
The libxml2 parser classes has the following limitations:
* -reportempty has no effect. libxml2 does not report empty element syntax.
* Incremental (push) parsing, ie. -final 0 is not supported.
* TclXML/libxml2 does not provide (DTD) validation, (WXS) schema validation or
Relax NG validation, although the libxml2 library does provide those functions.
These functions are provided by the TclDOM/libxml2 package, but only in a
"posteriori" fashion (ie. only after the document has been parsed).
* libxml2 supports XML Namespaces. The use of XML Namespaces can be queried, but
the declaration of a XML Namespace is not reported.