TclXML(n) TclXML(n)
Steve Ball'
__________________________________________________________________________________________________________________________________________________
NAME
::xml::parser - XML parser support for Tcl
SYNOPSIS
package require xml
package require parserclass
xml2.6
::xml::sgml::xml::tclparser
::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 imple-
mentation. 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 expat. 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
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 appli-
cation 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.
-baseurl -baseurl URI
Specifies the base URI for resolving relative URIs that may be used in the XML document to refer to external entities.
-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 evalu-
ated 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 evalu-
ated 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.
-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
-errrocommand -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 docu-
ment 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 applica-
tion 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 con-
figured 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.
-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 -char-
acterdatacommand 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 evalu-
ated 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 argu-
ments 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 ele-
ment 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 inter-
nal 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 documen-
tation 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.
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"
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 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.
Expat Parser Class
This section will discuss the Expat parser class.
SEE ALSO
TclDOM, a Tcl interface for the W3C Document Object Model.
KEYWORDS
Tcl Built-In Commands Tcl TclXML(n)