tnc - tnc is an expat parser object extension, that validates the XML stream
against the document DTD while parsing.
package require tdom
package require tnc
set parser [expat]
tnc $parser enable
adds the C handler set "tnc" to a tcl expat parser obj.
This handler set is a simple DTD validator. If the validator detects a
validation error, it sets the interp result, signals error and stops parsing.
There isn't any validation error recovering. As a consequence, only valid
documents are completely parsed.
This handler set has only three methods:
- tnc parserObj enable
Adds the tnc C handler set to a Tcl expat parser object.
- tnc parserObj remove
Removes the tnc validatore from the parser parserObj
and frees all
information, stored by it.
- tnc parserObj getValidateCmd
Returns a new created validation command, if one is available from the parser
command, otherwise it signals error. The name of the validation command is the
, if this optional argument was given, or a random
chosen name. A validation command is available in a parser command, if the
parser with tnc enabled was previously used, to parse an XML document with a
valid doctype declaration, a valid external subset, if one was given by the
doctype declaration, and a valid internal subset. The further document doesn't
need to be valid, to make the validation command available. The validation
command can only get received one time from the parser command. The created
validation command has this syntax:
validationCmd method ?args?
The valid methods are:
- validateDocument domDocument
- Checks, if the given domDocument is valid against the DTD information
represented by the validation command. Returns 1, if the document ist
valid, 0 otherwise. If the varName argument is given, then the
variable it names is set to the detected reason for the validation error
or to the empty string in case of a valid document.
- validateTree elementNode
- Checks, if the given subtree with domNode as root element is a
possible valid subtree of a document conforming to the DTD information
represented by the validation command. IDREF could not checked, while
validating only a subtree, but it is checked, that every known ID
attribute in the subtree is unique. Returns 1, if the subtree is OK, 0
otherwise. If the varName argument is given, then the variable it
names is set to the detected reason for the validation error or to the
empty string in case of a valid subtree.
- validateAttributes elementNode
- Checks, if there is an element declaration for the name of the
elementNode in the DTD represented by the validation command and,
if yes, if the attributes of the elementNode are conform to the
ATTLIST declarations for that element in the DTD. Returns 1, if the
attributes and there value types are OK, 0 otherwise. If the
varName argument is given, then the variable it names is set to the
detected reason for the validation error or to the empty string in case
the element has all its required attributes, only declared attributes and
the values of the attributes matches there type.
- Deletes the validation command and frees the memory used by it. Returns
the empty string.
The validation error reports could be much more informative and user-friendly.
The validator doesn't detect ambiguous content models (see XML recomendation
Section 3.2.1 and Appendix E). Most Java validators also doesn't, but handle
such content models right anyhow. Tnc does not; if your DTD has such ambiguous
content models, tnc can not used to validate documents against such (not
completely XML spec compliant) DTDs.
It isn't possible to validate XML documents with standalone="yes" in
the XML Declaration
Violations of the validity constraints Proper Group/PE Nesting and Proper
Conditional Section/PE Nesting are not detected. They could only happen inside
a invalid DTD, not in the content of a document.