NAME

       tnc  -  tnc  is  an expat parser object extension, that validates the XML stream against the document DTD
       while parsing.

SYNOPSIS

       package require tdom
       package require tnc

       set parser [expat]

       tnc $parser enable
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DESCRIPTION

       tnc 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 ?validateCmdName?

              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  validateCmdName,  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 ?varName?
                     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 ?varName?
                     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 ?varName?
                     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.

              delete Deletes the validation command and frees the memory used by it. Returns the empty string.

BUGS

       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.

KEYWORDS

       Validation, DTD