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