<?xml version="1.0" encoding="utf-8"?>
<manpage id="schema" cat="schema" title="schema">
  <namesection>
    <name>tdom::schema</name>
    <desc>Creates a schema validation command</desc>
  </namesection>

  <synopsis>
    <syntax>package require tdom

<cmd>tdom::schema</cmd> <m>?create?</m> <m>cmdName</m>
    </syntax>
  </synopsis>

  <section>
    <title>DESCRIPTION </title>    
    
    <p>Every call of this command creates a new validation command. A
    validation command has methods to define a schema and is able
    to validate XML data or to post-validate a tDOM DOM tree (and to
    some degree other kind of hierarchical data) against this
    schema.</p>

    <p>Also, a validation command may be used as argument to the
    <m>-validateCmd</m> option of the <m>dom parse</m> and the
    <m>expat</m> commands to enable validation additionally to what
    they do otherwise.</p>

    <p>The methods of created commands are:</p>

    <commandlist>
      <commanddef>
          <command><method>prefixns</method> <m>?prefixUriList?</m></command>
          <desc>This method controls prefix (or abbreviation) to
          namespace URI mapping. Wherever a namespace argument is
          expected in the schema command methods the
          &quot;prefix&quot; could be used instead of the namespace
          URI. If the list maps the same prefix to different namespace
          URIs, the first one wins. If there is no such prefix, the
          namespace argument is used literally as namespace URI. If
          the method is called without argument, it returns the
          current prefixUriList. If the method is called with the
          empty string, any namespace URI arguments are used
          literally. This is the default.
          </desc>
      </commanddef>

      <commanddef>
        <command><method>defelement</method> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This method defines the element <m>name</m> (optional in
        the namespace <m>namespace</m>) in the schema. The
        <m>definition script</m> is evaluated and defines the content
        model of the element. If the <m>namespace</m> argument is
        given, any <m>element</m> or <m>ref</m> references in the
        definition script not wrapped inside a <m>namespace</m>
        command are resolved in that namespace. If there is already a
        element definition for the name/namespace combination, the
        command raises error.</desc>
      </commanddef>

      <commanddef>
        <command><method>defelementtype</method> <m>typename</m> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This method defines the element type <m>typename</m>
        (optional in the namespace <m>namespace</m>) in the schema. If
        the element type is used in a definition script with the
        schema command elementtype, the validation engine expects an
        element named <m>name</m> (in the namespace <m>namespace</m>,
        if given) and the content model <m>definition script</m>.
        Defining element types seems only sensible if you really have
        elements with the same name and namespace but different
        content models. The <m>definition script</m> is evaluated and
        defines the content model of the element. If the
        <m>namespace</m> argument is given, any <m>element</m> or
        <m>ref</m> references in the definition script not wrapped
        inside a <m>namespace</m> command are resolved in that
        namespace. If there is already an elementtype definition for
        the name/namespace combination, the command raises error. The
        document element of any XML to validate cannot be a
        <m>defelementtype</m> defined element.</desc>
      </commanddef>

      <commanddef>
        <command><method>defpattern</method> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This method defines a (maybe complex) content particle
        with the <m>name</m> (optional in the namespace
        <m>namespace</m>) in the schema, to be used in other
        definition scripts with the definition command <m>ref</m>. The
        <m>definition script</m> is evaluated and defines the content
        model of the content particle. If the <m>namespace</m>
        argument is given, any <m>element</m> or <m>ref</m> references
        in the definition script not wrapped inside a <m>namespace</m>
        command are resolved in that namespace. If there is already a
        pattern definition for the name/namespace combination, the
        command raises error.</desc>
      </commanddef>

      <commanddef>
        <command><method>deftexttype</method> <m>name</m> <m>&lt;constraint script></m></command>
        <desc>This method defines a bundle of text constraints that
        can be referred to by <m>name</m> while defining constraints on
        text element or attribute values. If there is already a text
        type definition with this name, the command raises error. A
        text type must be defined before it can be used in schema
        definition scripts.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>start</method> <m>documentElement</m> <m>?namespace?</m></command>
        <desc>This method defines the name and namespace of the root
        element of a tree to validate. If this method is used, the
        root element must match for validity. If <m>start</m> is not
        used, any element defined by <m>defelement</m> may be the root
        of a valid document. The <m>start</m> method may be used
        several times with varying arguments during the lifetime of a
        validation command. If the command is called with just the
        empty string (and no namespace argument), the validation
        constraint for the root element is removed and any defined
        element will be valid as root of a tree to validate.</desc>
      </commanddef>

      <commanddef>
        <command><method>define</method> <m>&lt;definition script></m></command>
        <desc>This method allows to define several elements or patterns
        or a whole schema with one call. All schema command methods so
        far (<m>prefixns</m>, <m>defelement</m>,
        <m>defelementtype</m>, <m>defpattern</m>, <m>deftexttype</m> and
        <m>start</m>) are allowed top level in the <m>definition
        script</m>. The <m>define</m> method itself isn't allowed
        recursively.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>event</method> <m>(start|end|text)</m> <m>?event specific data?</m></command>
        <desc>This method allows the validation of hierarchical data against
        the content constraints of the validation command.

        <optlist>
          <optdef>
            <optname>start</optname>
            <optarg>name ?attributes? ?namespace? </optarg>
            <desc>Checks if the current validation state allows the
            element <m>name</m> in the <m>namespace</m> to start here.
            It raises error if not.</desc>
          </optdef>

          <optdef>
            <optname>end</optname>
            <desc>Checks if the current innermost open element may end
            there in the current state without violation of validation
            constraints. It raises error if not.</desc>
          </optdef>
          
          <optdef>
            <optname>text</optname>
            <optarg>text</optarg>
            <desc>Checks if the current validation state allows the
            given text content. It raises error if not.</desc>
          </optdef>
        </optlist>
        </desc>
      </commanddef>

      <commanddef>
        <command><method>validate</method> <m>&lt;XML string></m> <m>?objVar?</m></command>
        <desc>Returns true if the <m>&lt;XML string></m> is valid, or
        false, otherwise. If validation has failed and the optional
        <m>objVar</m> argument is given, the variable with that
        name is set to a validation error message. If the XML string
        is valid and the optional <m>objVar</m> argument is given,
        the variable with that name is set to the empty string.</desc>
      </commanddef>

      <commanddef>
        <command><method>validatefile</method> <m>filename</m> <m>?objVar?</m></command>
        <desc>Returns true if the content of <m>filename</m> is valid,
        or false, otherwise. The given file is feeded as binary stream
        to expat, therefore only US-ASCII, ISO-8859-1, UTF-8 or UTF-16
        encoded data will work with this method. If validation has
        failed and the optional <m>objVar</m> argument is given, the
        variable with that name is set to a validation error message.
        If the XML string is valid and the optional <m>objVar</m>
        argument is given, the variable with that name is set to the
        empty string.</desc>
      </commanddef>

      <commanddef>
        <command><method>validatechannel</method> <m>channel</m> <m>?objVar?</m></command>
        <desc>Returns true if the content read from the Tcl channel
        <m>channel</m> is valid, or false, otherwise. Since data read
        out of a Tcl channel is UTF-8 encoded, any misleading encoding
        declaration at the beginning of the data will lead to errors.
        If the validation fails and the optional <m>objVar</m>
        argument is given, the variable with that name is set to a
        validation error message. If the XML string is valid and the
        optional <m>objVar</m> argument is given, the variable with
        that name is set to the empty string.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>domvalidate</method> <m>domNode</m> <m>?objVar?</m></command>
        <desc>Returns true if the first argument is a valid tree, or
        false, otherwise. If validation has failed and the optional
        <m>objVar</m> argument is given, the variable with that name
        is set to a validation error message. If the dom tree is valid
        and the optional <m>objVar</m> argument is given, the variable
        with that name is set to the empty string. </desc>
      </commanddef>

      <commanddef>
        <command><method>reportcmd</method> <m>?cmd?</m></command>
        <desc>This method expects the name of a Tcl command to be
        called in case of validation error. The command will be
        called with two arguments appended: the schema command which
        raises the validation error, and a validation error code.

        <p>The possible error codes are:</p>
        <dl>
            <dt>MISSING_ELEMENT</dt><dd></dd>
            <dt>MISSING_TEXT</dt><dd></dd>
            <dt>UNEXPECTED_ELEMENT</dt><dd></dd>
            <dt>UNEXPECTED_ROOT_ELEMENT</dt><dd></dd>
            <dt>UNEXPECTED_TEXT</dt><dd></dd>
            <dt>UNKNOWN_ROOT_ELEMENT</dt><dd></dd>
            <dt>UNKNOWN_ATTRIBUTE</dt><dd></dd>
            <dt>MISSING_ATTRIBUTE</dt><dd></dd>
            <dt>INVALID_ATTRIBUTE_VALUE</dt><dd></dd>
            <dt>DOM_KEYCONSTRAINT</dt><dd></dd>
            <dt>DOM_XPATH_BOOLEAN</dt><dd></dd>
            <dt>INVALID_KEYREF</dt><dd></dd>
            <dt>INVALID_VALUE</dt><dd></dd>
            <dt>UNKOWN_GLOBAL_ID</dt><dd></dd>
            <dt>UNKOWN_ID</dt><dd></dd>
        </dl>
        <p> For more detailed information see section <ref
        refid="recovering">Recovering</ref>.</p>
        </desc>
      </commanddef>

      <commanddef>
        <command><method>delete</method></command>
        <desc>This method deletes the validation command.</desc>
      </commanddef>

      <commanddef>
          <command><method>info</method> <m>?args?</m></command>
          <desc>This method bundles methods to query the state of and
          details about the schema command.
          <optlist>
              <optdef>
                  <optname>validationstate</optname>
                  <desc>This method returns the state of the validation command
                  with respect to validation state. The possible return values
                  and their meanings are:
                  <dl>
                      <dt>READY</dt><dd>The validation command is ready to start
                      validation</dd>
                      <dt>VALIDATING</dt><dd>The validation command is in the
                      process of validating input.</dd>
                      <dt>FINISHED</dt><dd>The validation has finished, no further
                      events are expected.</dd>
                  </dl>
                  </desc>
              </optdef>
              <optdef>
                  <optname>vstate</optname>
                  <desc>This method is a shorter alias for validationstate; see there.</desc>
              </optdef>
              <optdef>
                  <optname>line</optname>
                  <desc>If the schema command is currently validating,
                  this method returns the line part of the parsing
                  position information, and the empty string in all
                  other cases. If the schema command is currently
                  post-validating a DOM tree, there may be no position
                  information stored at some or all nodes. The
                  empty string is returned in these cases.</desc>
              </optdef>
              <optdef>
                  <optname>column</optname>
                  <desc>If the schema command is currently validating
                  this method returns the column part of the parsing
                  position information, and the empty string in all
                  other cases. If the schema command is currently
                  post-validating a DOM tree, there may be no position
                  information stored at some or all nodes. The
                  empty string is returned in these cases.</desc>
              </optdef>
              <optdef>
                  <optname>domNode</optname>
                  <desc>If the schema command isn't currently
                  post-validating a DOM tree this method returns the
                  empty string. Otherwise, if the schema command waits
                  for the reportcmd script to finish while recovering
                  from a validation error it returns the node on which
                  the validation engine is currently looking at in
                  case the node is an ELEMENT_NODE or, if not, its
                  parent node. It is recommended that you do not use
                  this method. Or at least leave the DOM tree alone,
                  use it read-only.</desc>
              </optdef>
              <optdef>
                  <optname>nrForwardDefinitions</optname>
                  <desc>Returns how many elements, element types and
                  ref patterns are referenced that aren't defined so
                  far (summed together).</desc>
              </optdef>
              <optdef>
                  <optname>definedElements</optname>
                  <desc>Returns in no particular order the defined
                  elements in the grammar as list. If an element is
                  namespaced, its list entry will be itself a list with
                  two elements, with the name as first and the
                  namespace as second element.</desc>
              </optdef>
              <optdef>
                  <optname>definedElementtypes</optname>
                  <desc>Returns in no particular order the defined
                  element types in the grammar as list. If an element
                  type is namespaced, its list entry will be itself a
                  list with two elements, with the name as first and
                  the namespace as second element.</desc>
              </optdef>
              <optdef>
                  <optname>definedPatterns</optname>
                  <desc>Returns in no particular order the defined
                  named pattern in the grammar as list. If a named
                  pattern is namespaced, its list entry will be itself
                  a list with two elements, with the name as first and
                  the namespace as second element.</desc>
              </optdef>
              <optdef>
                  <optname>expected</optname>
                  <desc>Returns in no particular order all possible
                  next events (since the last successful event match,
                  if there was one) as a list. If an element is
                  namespaced its list entry will be itself a list with
                  two elements, with the name as first and the
                  namespace as second element. If text is a possible
                  next event, the list entry will be a two elements
                  list, with #text as first element and the empty
                  string as second. If an any element constraint is
                  possible. the list entry will be a two elements list,
                  with &lt;any> as first element and the empty string
                  as second. If an any element in a certain namespace
                  constraint is possible, the list entry will be a two
                  elements list, with &lt;any> as first element and
                  the namespace as second. If element end is a
                  possible event, the list entry will be a two elements
                  list with &lt;elementend> as first element and the
                  empty string as second element.</desc>
              </optdef>
              <optdef>
                  <optname>definition name ?namespace?</optname>
                  <desc>Returns the code that defines the given
                  element. The command raises error if there is no
                  definition of that element.
                  </desc>
              </optdef>
              <optdef>
                  <optname>typedefinition name ?namespace?</optname>
                  <desc>Returns the code that defines the given
                  element type definition. The command raises error if
                  there is no definition of that element.
                  </desc>
              </optdef>
              <optdef>
                  <optname>patterndefinition name ?namespace?</optname>
                  <desc>Returns the code that defines the given
                  pattern definition. The command raises error if
                  there is no definition of a pattern with that name
                  and, if given, namespace.
                  </desc>
              </optdef>
              <optdef>
                  <optname>vaction ?name|namespace|text?</optname>
                  <desc><p>This method returns useful information only if
                  the schema command waits for the reportcmd script to
                  finish while recovering from a validation error.
                  Otherwise it returns NONE.</p>
                  <p>If the command is called without the optional
                  argument the possible return values and their
                  meanings are:</p>
                  <dl>
                      <dt>NONE</dt><dd>The schema command currently
                      does not recover from a validation event.</dd>
                      <dt>MATCH_ELEMENT_START</dt><dd>Element start event, which includes looking for missing or unknown attributes.</dd>
                      <dt>MATCH_ELEMENT_END</dt><dd>Element end event.</dd>
                      <dt>MATCH_TEXT</dt><dd>Validating text between tags.</dd>
                      <dt>MATCH_ATTRIBUTE_TEXT</dt><dd>Attribute text value constraint check</dd>
                      <dt>MATCH_GLOBAL</dt><dd>Checking global IDs</dd>
                      <dt>MATCH_DOM_KEYCONSTRAINT</dt><dd>Checking domunique constraint</dd>
                      <dt>MATCH_DOM_XPATH_BOOLEAN</dt><dd>Checking domxpathboolean constant</dd>
                  </dl>
                  <p>If called with one of the possible optional
                  arguments, the command returns detail information
                  depending on current action.</p>
                  <dl>
                      <dt>name</dt><dd>Returns the name of the element
                      that has to match in case of
                      MATCH_ELEMENT_START. Returns the name of the
                      closed element in case of MATCH_ELEMENT_END.
                      Returns the name of the attribute in case of
                      MATCH_ATTRIBUTE_TEXT. Returns the name of the
                      parent element in case of MATCH_TEXT.</dd>
                      
                      <dt>namespace</dt><dd>Returns the namespace of
                      the element that has to match in case of
                      MATCH_ELEMENT_START. Returns the namespace of the
                      closed element in case of MATCH_ELEMENT_END.
                      Returns the namespace of the attribute in case
                      of MATCH_ATTRIBUTE_TEXT. Returns the namespace of
                      the parent element in case of MATCH_TEXT.</dd>
                      
                      <dt>text</dt><dd>Returns the text to match in
                      case of MATCH_TEXT. Returns the value of the
                      attribute in case of MATCH_ATTRIBUTE_TEXT.</dd>
                  </dl>
                  </desc>
              </optdef>
              <optdef>
                  <optname>stack top|inside|associated</optname>
                  <desc>In Tcl scripts evaluated by validation this method
                  provides information about the current validation stack.
                  Called outside this context the method returns the empty
                  string.
                  <optlist>
                      <optdef>
                          <optname>top</optname>
                          <desc>Returns the element whose content is currently
                          checked (the open element tag at this moment).
                          </desc>
                      </optdef>
                      
                      <optdef>
                          <optname>inside</optname>
                          <desc>Returns all currently open elements as a list.</desc>
                      </optdef>
                      
                      <optdef>
                          <optname>associated</optname>
                          <desc>Returns the data associated with the
                          current top most stack content particle or
                          the empty string if there isn't any.
                          </desc>
                      </optdef>
                  </optlist>
                  </desc>
              </optdef>
          </optlist>
          </desc>
      </commanddef>
      
      <commanddef>
        <command><method>reset</method></command>
        <desc>This method resets the validation command into state
        READY (while preserving the defined grammar).</desc>
      </commanddef>

    </commandlist>
  </section>

  <section>
    <title>Schema definition scripts</title>

    <p>Schema definition scripts are ordinary Tcl scripts evaluated in
    the namespace tdom::schema. The schema definition commands listed
    below in this Tcl namespace allow the definition of a wide variety
    of document structures. Every schema definition command
    establishes a validation constraint on the content which has to
    match or must be optional to qualify the content as valid. It is a
    validation error if there is additional (not matched) content.
    White-space-only text (in the XML sense of white space) between
    any different tags is ignored, with the exception of text only
    elements (for which even white-space-only text will be considered
    as significant content).</p>

    <p>The schema definition commands are:</p>

    <commandlist>
      <commanddef>
        <command><method>element</method> <m>name</m> <m>?quant?</m> <m>?&lt;definition script>?</m></command>
        <desc>If the optional argument <m>definition script</m> is not
        given this command refers to the element defined with
        <m>defelement</m> with the name <m>name</m> in the current
        context namespace. If the <m>defelement script</m> argument is
        given, the validation constraint expects an element with the
        name <m>name</m> in the current namespace with content
        "locally" defined by the <m>definition script</m>. Forward
        references to so far not defined elements or patterns or other
        local definitions of the same name inside the <m>definition
        script</m> are allowed. If a forward referenced element is not
        defined until validation, only an empty element with name
        <m>name</m> and namespace <m>namespace</m> and no attributes
        matches. </desc>
      </commanddef>

      <commanddef>
        <command><method>elementtype</method> <m>name</m> <m>?quant?</m></command>
        <desc>This command refers to the element defined with
        <m>defelementtype</m> with the type name <m>name</m> in the
        current context namespace. Forward references to so far not
        defined element types or recursive references are allowed. If
        a forward referenced element type is not defined until
        validation any empty element without attributes will be
        accepted.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>ref</method> <m>name</m> <m>?quant?</m></command>
        <desc>This command refers to the content particle defined with
        <m>defpattern</m> with the name <m>name</m> in the current
        context namespace. Forward references to a so far not defined
        pattern and recursive references are allowed. If a forward
        referenced pattern is not defined until validation no content
        whatsoever is expected ("empty match").</desc>
      </commanddef>

      <commanddef>
        <command><method>group</method> <m>?quant?</m> <m>&lt;definition script></m></command>
        <desc>This method allows to group a sequence of content
        particles defined by the <m>definition script></m>, which have
        to match in this sequence order.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>choice</method> <m>?quant?</m> <m>&lt;definition script></m></command>
        <desc>This schema constraint matches if one of the top level
        content particles defined by the <m>definition script></m>
        matches. If one of this top level content particle is optional
        this constraint matches the "empty match".
        </desc>
      </commanddef>

      <commanddef>
        <command><method>interleave</method> <m>?quant?</m> <m>&lt;definition script></m></command>
        <desc>This schema constraint matches after every of the required
        top level content particles defined by the <m>definition
        script></m> have matched (and, optional, some or all other) in
        any arbitrary order.</desc>
      </commanddef>

      <commanddef>
        <command><method>mixed</method> <m>?quant?</m> <m>&lt;definition script></m></command>
        <desc>This schema constraint matches for any text (including the
        empty one) and every top level content particle defined by the
        <m>definition script></m> with default quantifier *.</desc>
      </commanddef>

      <commanddef>
        <command><method>text</method> <m>?&lt;constraint script>|"type" typename?</m></command>
        <desc>Without the optional constraint script this validation
        constraint matches every string (including the empty one).
        With <m>constraint script</m> or with a given text type
        argument a text matching this script or the text type is
        expected. </desc>
      </commanddef>

      <commanddef>
        <command><method>any</method> <m>?namespace?</m> <m>?quant?</m></command>
        <desc>The any command matches every element (in the namespace
        <m>namespace</m>, if that is given) (with whatever attributes)
        or subtree, no matter if known within the schema or not.
        Please note that in case of no <m>namespace</m> argument is
        given that means that the quantifier * and + will eat up any
        elements until the enclosing element ends. If you really have
        a namespace that looks like a valid tDOM schema quantifier
        you will have to spell out always both arguments.</desc>
      </commanddef>

      <commanddef>
        <command><method>attribute</method> <m>name</m> <m>?quant?</m> <m>(?&lt;constraint script>|"type" typename?)</m></command>
        <desc>The attribute command defines an attribute (in no
        namespace) to the enclosing element. The first definition of
        <m>name</m> inside an element definition wins; later
        definitions of the same name are silently ignored. After the
        <m>name</m> argument there may be one of the quantifiers ? or
        !. If there is, it will be used. Otherwise the attribute will
        be required (must be present in the XML source). If there is
        one argument more this argument is evaluated as constraint
        script, defining the value constraints of the attribute.
        Otherwise, if there are two more arguments and the first of
        them is the bare-word "type" the following argument is used as
        a text type name. This command is only allowed at top level in
        the definition script of an defelement/element script.</desc>
      </commanddef>

      <commanddef>
        <command><method>nsattribute</method> <m>name</m> <m>namespace</m> <m>?quant?</m> <m>(?&lt;constraint script>|"type" typename?)</m></command>
        <desc>This command does the same as the command
        <m>attribute</m>, for the attribute <m>name</m> in the
        namespace <m>namespace</m>.</desc>
      </commanddef>

      <commanddef>
        <command><method>namespace</method> <m>URI</m> <m>&lt;definition script></m></command>
        <desc>Evaluates the <m>definition script</m> with context
        namespace <m>URI</m>. Every element, element type or ref
        command name will be looked up in the namespace <m>URI</m>,
        and local defined elements will be in that namespace. An
        empty string as <m>URI</m> means no namespace.</desc>
      </commanddef>

      <commanddef>
        <command><method>tcl</method> <m>tclcmd</m> <m>?arg arg ...?</m></command>
        <desc>Evaluates the Tcl script <m>tclcmd arg arg ... </m>.
        This validation command is only allowed in strict sequential
        context (not in choice, mixed and interleave). If the return
        code is something else than TCL_OK, this is an error (which
        is not catched and reported by reportcmd).</desc>
      </commanddef>

      <commanddef>
        <command><method>self</method></command>
        <desc>Returns the schema command.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>associate</method> <m>data</m></command>
        <desc>This command is only allowed top-level inside definition
        scripts of the element, elementtype, pattern or interleave
        content particles. Associates the <m>data</m> given as argument
        with the currently defined content particle and may be
        requested in scripts evaluated while validating the content of
        that particle with the schema command method call <m>info
        stack associated</m>.</desc>
      </commanddef>

      <commanddef>
        <command><method>domunique</method> <m>selector</m> <m>fieldlist</m> <m>?name?</m> <m>?"IGNORE_EMPTY_FIELD_SET"|("EMPTY_FIELD_SET_VALUE" emptyFieldSetValue)?</m></command>
        <desc>If not postvalidating a DOM tree with <m>domvalidate</m>
        this constraint always matches. If postvalidating this
        constraint resembles the xsd key/keyref mechanism. The
        <m>selector</m> argument may be any valid XPath expression
        (without the xsd limits). Several <m>domunique</m> commands
        within one element definition are allowed. They are checked in
        definition order. The argument name is available in the
        recovering script per <m>info vaction name</m>. If the
        <m>fieldlist</m> does not select something for a node of the
        result set of the <m>selector</m> the key value will be the
        empty string by default. If the arguments
        <m>EMPTY_FIELD_SET_VALUE &lt;value></m> are given an empty
        node set will have the key value <m>value</m>. If instead the
        flag <m>IGNORE_EMPTY_FIELD_SET</m> flag is given an empty
        node set result will not have any key value.</desc>
      </commanddef>

      <commanddef>
        <command><method>domxpathboolean</method> <m>XPath_expr</m> <m>?name?</m></command>
        <desc><p>If not postvalidating a DOM tree with
        <m>domvalidate</m> this constraint always matches. If
        postvalidating the <m>XPath_expr</m> argument is evaluated
        (with the node matching the schema parent of the
        <m>domxpathboolean</m> command as context node). The
        constraint maches if the result of this XPath expression,
        converted to boolean by XPath rules, is true. Several
        <m>domxpathboolean</m> commands within one element definition
        are allowed. They are checked in definition order.</p>

        <p>This enables checks depending on more than one element. Consider</p>

        <example>
tdom::schema s
s define {
    defelement doc {
        element a ! text
        element b ! text
        element c ! text
        domxpathboolean "a * b * c &gt;= 20000" volume
        domxpathboolean "a &gt; b and b &gt; c" sequence
    }
}
        </example>
        </desc>
      </commanddef>

      <commanddef>
        <command><method>prefixns</method> <m>?prefixUriList?</m></command>
        <desc>This defines a prefix to namespace URI mapping exactly
        as a <i>schemacmd prefixns</i> would. It is meant as top-level
        command of a <i>schemacmd define</i> script. This command is
        not allowed nested in another definition script command and
        will raise error, if you call it there.</desc>
      </commanddef>

      <commanddef>
        <command><method>defelement</method> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This defines an element exactly as a <i>schemacmd
        defelement</i> call would. It is meant as top-level command of a
        <i>schemacmd define</i> script. This command is not allowed
        nested in another definition script command and will raise
        error, if you call it there.</desc>
      </commanddef>

      <commanddef>
        <command><method>defelementtype</method> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This defines an elementtype exactly as a <i>schemacmd
        defelementtype</i> call would. It is meant as top-level
        command of a <i>schemacmd define</i> script. This command is
        not allowed nested in another definition script command and
        will raise error, if you call it there.</desc>
      </commanddef>

      <commanddef>
        <command><method>defpattern</method> <m>name</m> <m>?namespace?</m> <m>&lt;definition script></m></command>
        <desc>This defines a named pattern exactly as a <i>schemacmd
        defpattern</i> call would. It is meant as top-level command of a
        <i>schemacmd define</i> script. This command is not allowed
        nested in another definition script command and will raise
        error, if you call it there.</desc>
      </commanddef>

      <commanddef>
        <command><method>deftexttype</method> <m>name</m> <m>&lt;constraint script></m></command>
        <desc>This defines a named bundle of text constraints exactly
        as a <i>schemacmd deftexttype</i> call would. It is meant as
        top-level command of a <i>schemacmd define</i> script. This
        command is not allowed nested in another definition script
        command and will raise error, if you call it there.</desc>
      </commanddef>
      
      <commanddef>
        <command><method>start</method> <m>name</m> <m>?namespace?</m></command>
        <desc>This command works exactly as a <i>schemacmd start</i>
        call would. It is meant as top-level command of a <i>schemacmd
        define</i> script. This command is not allowed nested in
        another definition script command and will raise error, if you
        call it there.</desc>
      </commanddef>
    </commandlist>
    
  </section>

  <section>
    <title>Quantity specifier</title>

    <p>Several schema definition commands expect a quantifier as
    one of their arguments which determines how often the content
    particle specified by the command is expected. The valid values
    for a <m>quant</m> argument are:</p>

    <optlist>
      <optdef>
        <optname>!</optname>
        <desc>The content particle has to occur exactly once in valid
        documents.</desc>
      </optdef>
    
      <optdef>
        <optname>?</optname>
        <desc>The content particle may not occur more than once in
        valid documents - the particle is optional.</desc>
      </optdef>
    
      <optdef>
        <optname>*</optname>
        <desc>The content particle may occur zero or more times in a
        row in valid documents.</desc>
      </optdef>
    
      <optdef>
        <optname>+</optname>
        <desc>The content particle may occur one or more times in a
        row in valid documents.</desc>
      </optdef>
    
      <optdef>
        <optname>n</optname>
        <desc>The content particle must occur n times in a row in
        valid documents. The quantifier must be an integer greater
        zero.</desc>
      </optdef>
    
      <optdef>
        <optname>{n m}</optname> <desc>The content particle must occur
        at least n and at most m times in a row in valid documents.
        The quantifier must be a Tcl list with two elements. Both
        elements must be integers, with n >= 0 and n &lt; m.</desc>
      </optdef>
    </optlist>

    <p>If an optional quantifier is not given, it defaults to * in
    case of the <m>mixed</m> command and to ! for all other commands.</p>
  </section>

  <section>
    <title>Text constraint scripts</title>

    <p>Text (parsed character data, as XML calls it) sometimes has to
    be of a certain kind or comply with certain rules to be valid. The
    text constraint script arguments to text, attribute, nsattribute
    and deftexttype commands are evaluated in the Tcl namespace
    <m>tdom::schema::text</m> namespace and allow the ensuing text
    constraint commands to check text for certain properties. The
    commands are defined in the Tcl namespace
    <m>tdom::schema::text</m>. They raise error in case they are
    called outside of a text constraint script.</p>

    <p>A few of the ensuing text type commands are exposed as general
    Tcl commands. They are defined in the namespace tdom::type and are
    called as documented below with the text to check appended to the
    argument list. They return a logical value. Please note that the
    commands may not accept starting or ending white space. If a
    command is available in the tdom::type namespace is recorded in
    its documentation.
    </p>

    <subsection>
        <title>The tcl text constraint command</title>
        <p>The <m>tcl</m> text constraint command dispatches the check
        to an arbitrary Tcl command, thus enable any programmable
        decision rules.</p>
        <commandlist>
            <commanddef>
                <command><cmd>tcl</cmd> <m>tclcmd</m> <m>?arg arg ...?</m></command>
                <desc>Evaluates the Tcl script <m>tclcmd arg arg ... </m> and
                the text to validate appended to the argument list. The return
                value of the Tcl command is interpreted as a boolean.</desc>
            </commanddef>
        </commandlist>
    </subsection>

    <subsection>
        <title>Basic XML types</title>
        <commandlist>
            <commanddef>
                <command><cmd>name</cmd></command>
                <desc>This text constraint matches if the text value
                matches the XML name production
                <url>https://www.w3.org/TR/xml/#NT-Name</url>. This
                means that the text value must start with a letter,
                underscore (_), or colon (:), and may contain only
                letters, digits, underscores (_), colons (:), hyphens
                (-), and periods (.).</desc>
            </commanddef>
            <commanddef>
                <command><cmd>ncname</cmd></command>
                <desc>This text constraint matches if the text value
                matches the XML ncname production
                <url>https://www.w3.org/TR/xml-names/#NT-NCName</url>.
                This means that the text value must start with a
                letter or underscore (_), and may contain only
                letters, digits, underscores (_), hyphens (-), and
                periods (.) (The only difference to the name
                constraint is that colons are not permitted.)</desc>
            </commanddef>
            <commanddef>
                <command><cmd>qname</cmd></command>
                <desc>This text constraint matches if the text value
                matches the XML qname production
                <url>https://www.w3.org/TR/xml-names/#NT-QName</url>.
                This means that the text value is either a ncname or
                two ncnames joined by a colon (:).</desc>
            </commanddef>
            <commanddef>
                <command><cmd>nmtoken</cmd></command>
                <desc>This text constraint matches if the text value
                matches the XML nmtoken production
                <url>https://www.w3.org/TR/xml/#NT-Nmtoken</url></desc>
            </commanddef>
            <commanddef>
                <command><cmd>nmtokens</cmd></command>
                <desc>This text constraint matches if the text value
                matches the XML nmtokens production
                <url>https://www.w3.org/TR/xml/#NT-Nmtokens</url></desc>
            </commanddef>
        </commandlist>
    </subsection>

    <subsection>
        <title>Basic type tests</title>
        <p>
        </p>
        <commandlist>
            <commanddef>
                <command><cmd>integer</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches if the text value could be
                parsed as an integer. If the optional argument to the command
                is <m>tcl</m>, everything that returns TCL_OK if feeded into
                Tcl_GetInt() matches. If the optional argument to the command
                is <m>xsd</m>, the constraint matches if the value is a
                valid xsd:integer. Without argument <m>xsd</m> is the
                default.</desc>
            </commanddef>

            <commanddef>
                <command><cmd>negativeInteger</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches the same text values as the
                <m>integer</m> text constraint (see there), with the additional
                constraint, that the value must be &lt; zero.</desc>
            </commanddef>
            
            <commanddef>
                <command><cmd>nonNegativeInteger</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches the same text values as the
                <m>integer</m> text constraint (see there), with the additional
                constraint, that the value must be &gt;= zero.</desc>
            </commanddef>

            <commanddef>
                <command><cmd>nonPositiveInteger</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches the same text values as the
                <m>integer</m> text constraint (see there), with the additional
                constraint, that the value must be &lt;= zero.</desc>
            </commanddef>

            <commanddef>
                <command><cmd>positiveInteger</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches the same text values as the
                <m>integer</m> text constraint (see there), with the additional
                constraint, that the value must be &gt; zero.</desc>
            </commanddef>

            <commanddef>
                <command><cmd>number</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches if the text value could be
                parsed as a number. If the optional argument to the command is
                <m>tcl</m>, everything that returns TCL_OK if feeded into
                Tcl_GetDouble() matches. If the optional argument to the command
                is <m>xsd</m>, the constraint matches if the value is a
                valid xsd:decimal. Without argument <m>xsd</m> is the
                default.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>boolean</cmd> <m>?(xsd|tcl)?</m></command>
                <desc>This text constraint matches if the text value could be
                parsed as a boolean. If the optional argument to the command is
                <m>tcl</m>, everything that returns TCL_OK if feeded into
                Tcl_GetBoolean() matches. If the optional argument to the command
                is <m>xsd</m>, the constraint matches if the value is a
                valid xsd:boolean. Without argument <m>xsd</m> is the
                default.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>date</cmd></command>
                <desc>This text constraint matches if the text value is
                a xsd:date, which is basically like an ISO 8601 date of
                the form YYYY-MM-DD, with optional time zone part
                (either the letter Z or plus (+) or minus (-) followed
                by hh:mm and with maximum allowed positive or negative
                time zone 14:00). It follows the date rules of the
                Gregorian calendar for all dates. A preceding minus
                sign for bce dates is allowed. There is no year 0. The
                year may have more than 4 digits, but only if needed
                (no extra leading zeros). This is available as common
                Tcl command tdom::type::date.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>time</cmd></command>
                <desc>This text constraint matches if the text value is
                a xsd:time, which is basically like an ISO 8601 time of
                the form hh:mm:ss with optional time zone part. The
                time zone part follow the rules of the <m>date</m>
                command; see there. All three parts of the time value
                (hours, minutes, seconds) must be spelled out with 2
                digits. Additional fractional seconds (with a point
                ('.') as separator) are allowed, but not just a
                dangling point. The time value 24:00:00 (without
                fractional part) is allowed. This is available as
                common Tcl command tdom::type::time.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>dateTime</cmd></command>
                <desc>This text constraint matches if the text value
                is a xsd:dateTime, which is basically like an ISO 8601
                date time of the form YYYY-MM-DDThh:mm:ss with
                optional time zone part. The date and time zone parts
                follows the rules of the <m>date</m> and <m>time</m>
                command; see there. The time part (including the
                signaling 'T' character) is mandatory. This is
                available as common Tcl command
                tdom::type::dateTime.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>duration</cmd></command>
                <desc>This text constraint matches if the text value is
                a xsd:duration, which is basically like an ISO 8601
                duration of the form PnYnMnDTnHnMnS. All parts other
                than the starting P and - if one of H, M or S is given
                - T are optional. In case the following sign letter is
                S, n may be a decimal (with at least one digit before
                and after the dot), otherwise it must be a (positive)
                integer. This is available as common Tcl command
                tdom::type::duration.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>base64</cmd></command>
                <desc>This text constraint matches if text is valid according to
                RFC 4648.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>hexBinary</cmd></command>
                <desc>This text constraint matches if text is a sequence of
                binary octets in hexadecimal encoding, where each binary octet
                is a two-character hexadecimal number. Lowercase and uppercase
                letters A through F are permitted.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>unsignedByte</cmd></command>
                <desc>This text constraint matches if the text value is a
                xsd:unsignedByte. This is an integer between 0 and 255, both
                included, optionally preceded by a + sign and leading
                zeros.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>unsignedShort</cmd></command>
                <desc>This text constraint matches if the text value is a
                xsd:unsignedShort. This is an integer between 0 and 65535,
                both included, optionally preceded by a + sign and leading
                zeros.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>unsignedInt</cmd></command>
                <desc>This text constraint matches if the text value is a
                xsd:unsignedInt. This is an integer between 0 and 4294967295,
                both included, optionally preceded by a + sign and leading
                zeros.</desc>
            </commanddef>
            <commanddef>
                <command><cmd>unsignedLong</cmd></command>
                <desc>This text constraint matches if the text value is a
                xsd:unsignedLong. This is an integer between 0 and
                18446744073709551615, both included, optionally preceded by a
                + sign and leading zeros.</desc>
            </commanddef>
        </commandlist>
    </subsection>

    <subsection>
        <title>Logical constructs</title>
        <commandlist>
        <commanddef>
            <command><cmd>oneOf</cmd> <m>&lt;constraint script></m></command>
            <desc>This text constraint matches if one of the text
            constraints defined in the argument <m>constraint script</m>
            matches the text. It stops after the first matches and probes the
            text constraints in the order of definition.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>allOf</cmd> <m>&lt;constraint script></m></command>
            <desc>This text constraint matches if all of the text
            constraints defined in the argument <m>constraint script</m>
            matches the text. It stops after the first match failure and
            probes the text constraints in the order of definition. Since
            the schema definition command <m>text</m> also expects all
            text constraints to match the text constraint, <m>allOf</m> is
            useful mostly in connection with the <m>oneOf</m> text constraint
            command.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>not</cmd> <m>&lt;constraint script></m></command>
            <desc>This text constraint matches if none of the text
            constraints defined in the argument <m>constraint
            script</m> matches the text. It stops after the first
            matching constraint in the <m>constraint script</m> and
            reports validation error. The text constraints in the
            <m>constraint script</m> are probed in the order of
            definition.</desc>
        </commanddef>
        </commandlist>
    </subsection>

    <subsection>
        <title>Constraints on processed text value</title>
        <commandlist>
            <commanddef>
            <command><cmd>whitespace</cmd> <m>(preserve|replace|collapse)</m> <m>&lt;constraint script></m></command>
            <desc>This text constraint command does white-space (#x20
            (space, ' '), #x9 (tab, \t), #xA (linefeed, \n), and #xD
            (carriage return, \r) normalization to the text value and
            checks the resulting text with the text constraints of the
            constraint script argument. The normalization method
            <m>preserve</m> keeps everything as it is; this is another way
            to say <m>allOf</m>. The <m>replace</m> normalization method
            replaces any single white-space character (as above) to a
            space. The <m>collapse</m> normalization method removes all
            leading and trailing white-space, and all the other sequences of
            contiguous white-space are replaced by a single space.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>split</cmd> <m>?type ?args??</m><m>&lt;constraint script></m></command>
            <desc><p>This text constraint command splits the text to test
            into a list of values and tests all elements of that list for
            the text constraints in the evaluated <m>constraint
            script></m>.</p>
            <p>The available types are:</p>
            <dl>
                <dt>whitespace</dt><dd>The text to split is stripped
                of all white space at start and end and splitted into
                a list at any successive white space.</dd>
                <dt>tcl tclcmd ?arg ...?</dt><dd>The text to split is
                handed to the <m>tclcmd</m>, which is evaluated on
                global level, appended with every given arg and the
                text to split as last argument. This call must return
                a valid Tcl list whose elements are tested.</dd>
            </dl>
            <p>The default in case no split type argument is given is
            <m>whitespace</m>.</p></desc>
        </commanddef>
        <commanddef>
            <command><cmd>strip</cmd> <m>&lt;constraint script></m></command>
            <desc>This text constraint command tests all text constraints
            in the evaluated <m>constraint script></m> with the text to
            test stripped of all white space at start and end.</desc>
        </commanddef>
        </commandlist>
    </subsection>

    <subsection>
        <title>Various other string properties</title>
        <commandlist>
        <commanddef>
            <command><cmd>fixed</cmd> <m>value</m></command>
            <desc>The text constraint only matches if the text value is
            string equal to the given value.</desc>
        </commanddef>
        
        <commanddef>
            <command><cmd>enumeration</cmd> <m>list</m></command>
            <desc>This text constraint matches if the text value is equal to
            one element (respecting case and any white-space) of the
            argument <m>list</m>, which has to be a valid Tcl list.
            </desc>
        </commanddef>
        <commanddef>
            <command><cmd>match</cmd> <m>?-nocase?</m> <m>glob_style_match_pattern></m></command>
            <desc>This text constraint matches if the text value matches the
            glob style pattern given as argument. It follows the rules of
            the Tcl [string match] command, see
            <url>https://www.tcl.tk/man/tcl8.6/TclCmd/string.htm#M35</url>.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>regexp</cmd> <m>expression</m></command>
            <desc>This text constraint matches if the text value matches the
            regular expression given as argument. <url>https://www.tcl.tk/man/tcl8.6/TclCmd/re_syntax.htm</url> describes the regular expression syntax</desc>
        </commanddef>
        <commanddef>
            <command><cmd>length</cmd> <m>length</m></command>
            <desc>This text constraint matches if the length of the text
            value (in characters, not bytes) is <m>length</m>. The
            length argument must be a positive integer or zero.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>maxLength</cmd> <m>length</m></command>
            <desc>This text constraint matches if the length of the text
            value (in characters, not bytes) is at most <m>length</m>. The
            length argument must be an integer greater zero.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>minLength</cmd> <m>length</m></command>
            <desc>This text constraint matches if the length of the text
            value (in characters, not bytes) is at least <m>length</m>.
            The length argument must be an integer greater zero.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>id</cmd> <m>?keySpace?</m></command>
            <desc>This text constraint command marks the text as a
            document wide ID (to be referenced by an idref). Every ID
            value within a document must be unique. It isn't an error if
            the ID isn't actually referenced within the document. The
            optional argument <m>keySpace</m> does all this for a named
            key space. The key space "" (the empty sting) is another key
            space then the <m>id</m> command without keySpace
            argument.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>idref</cmd> <m>?keySpace?</m></command>
            <desc>This text constraint command expects the text to be a
            reference to an ID within the document. The referenced ID may
            appear later in the document, that the reference. Several
            references within the document to one ID are possible.</desc>
        </commanddef>
        </commandlist>
    </subsection>
  </section>

  <section>
    <title>Local key constraints</title>

    <p>Document wide uniqueness and foreign key constraints are
    available with the text constraint commands id and idref.
    Keyspaces allow for sub-tree local uniqueness and foreign key
    constraints.</p>

    <commandlist>
        <commanddef>
            <command><cmd>keyspace</cmd> <m>&lt;names list></m> <m>&lt;constraint script></m></command>
            <desc>Any number of keyspaces are possible. A keyspace is
            either active or not. An inside a <m>constraint
            script</m> called keyspace with the same name does
            nothing.</desc>
        </commanddef>
    </commandlist>

    <p>This text constraint commands work with keyspaces:</p>

    <commandlist>
        <commanddef>
            <command><cmd>key</cmd> <m>&lt;name></m></command>
            <desc>If the keyspace with the name <m>&lt;name></m> is
            not active the constraint always matches. If the keyspace
            is active, reports error if there is already a key with
            the value. Otherwise it stores the value as key in this
            keyspace and matches.</desc>
        </commanddef>
        <commanddef>
            <command><cmd>keyref</cmd> <m>&lt;name></m></command>
            <desc>If the keyspace with the name <m>&lt;name></m> is not
            active always matches. If the keyspace is active then
            reports error if there is still no key as the value at the
            end of the keyspace <m>&lt;name></m>. Otherwise, it
            matches.</desc>
        </commanddef>
    </commandlist>
    
  </section>

  <section id="recovering">
      <title>Recovering</title>

      <p>By default the validation engine stops at the first detected
      validation violation and reports that finding. It does so by
      return false (and sets, if given, the result variable with an
      error message) in case the schema command itself is used to
      validate input. If the schema command is used by a SAX parser or
      the DOM parser, it does so by throwing error.</p>

      <p>If a <m>reportcmd</m> is set this command is called on global
      level appended with the schema command and an error type as
      arguments in case a validation violation is detected. Then the
      validation recovers from the error and continues. For some
      validation errors the recover strategy can be determined with
      the script result of the reportcmd.</p>

      <p>With a <m>reportcmd</m> (which does not throw error if
      called) the validation engine will never report validation
      failure to its caller. The validation engine recovers,
      continues, and reports the next error (if occuring) and so on
      until the end of the input. The schema command will return true
      and the SAX parser and DOM builder will process normally until
      the end of the input, as if there had not been a validation
      error.</p>

      <p>Please note that this happens only for validation errors. It
      is not possible to recover from well-formedness errors. If the
      input is not well-formed, the schema command returns false and
      sets (if given) the result variable with an error message about
      the well-formedness error.</p>

      <p>If the <m>reportcmd</m> throws error while called by the
      validation engine then validation stops and the schema command
      throws error with the error message of the script.</p>

      <p>While validating basically three events can happen: an
      element start tag has to match, a piece of text has to match or
      an element end tag has to match. The method <m>info vaction</m>
      called in the recovering script or any script code called from
      there returns, which event has triggered the error report
      (MATCH_ELEMENT_START, MATCH_TEXT, MATCH_ELEMENT_END,
      respectively). While the command walks throu the schema looking
      whether the event matches other, data driven events (as, for example
      checking, if any keyref within a keyspace exists) may happen.</p>

      <p>Several of the validation error codes, appended as second
      argument to the <m>reportcmd</m> calls, may happen at more than
      one kind of validation event. The <m>info vaction</m> method and
      its subcommands provide information about the current validation
      event, if called from the report command.</p>

      <p>If a structural validation error happens, the default
      recovering strategy is to ignore any following (or missing)
      content within the current subtree and to continue with the
      element end event of the subtree.</p>

      <p>Returning "ignore" from the recovering script in case of
      error type MISSING_ELEMENT recovers by ignoring the failed
      contraint and continues to match the event further against the
      schema.</p>

      <p>Returning "vanish" from the recover script in case of the
      error types MISSING_ELEMENT and UNEXPECTED_ELEMENT recovers by
      ignoring the event.</p>
      
  </section>

  <section>
    <title>Examples</title>

    <p>The XML Schema Part 0: Primer Second Edition
    (<url>https://www.w3.org/TR/xmlschema-0/</url>) starts with this
    example schema:</p>

    <example>
&lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  &lt;xsd:annotation>
    &lt;xsd:documentation xml:lang="en">
     Purchase order schema for Example.com.
     Copyright 2000 Example.com. All rights reserved.
    &lt;/xsd:documentation>
  &lt;/xsd:annotation>

  &lt;xsd:element name="purchaseOrder" type="PurchaseOrderType"/>

  &lt;xsd:element name="comment" type="xsd:string"/>

  &lt;xsd:complexType name="PurchaseOrderType">
    &lt;xsd:sequence>
      &lt;xsd:element name="shipTo" type="USAddress"/>
      &lt;xsd:element name="billTo" type="USAddress"/>
      &lt;xsd:element ref="comment" minOccurs="0"/>
      &lt;xsd:element name="items"  type="Items"/>
    &lt;/xsd:sequence>
    &lt;xsd:attribute name="orderDate" type="xsd:date"/>
  &lt;/xsd:complexType>

  &lt;xsd:complexType name="USAddress">
    &lt;xsd:sequence>
      &lt;xsd:element name="name"   type="xsd:string"/>
      &lt;xsd:element name="street" type="xsd:string"/>
      &lt;xsd:element name="city"   type="xsd:string"/>
      &lt;xsd:element name="state"  type="xsd:string"/>
      &lt;xsd:element name="zip"    type="xsd:decimal"/>
    &lt;/xsd:sequence>
    &lt;xsd:attribute name="country" type="xsd:NMTOKEN"
                   fixed="US"/>
  &lt;/xsd:complexType>

  &lt;xsd:complexType name="Items">
    &lt;xsd:sequence>
      &lt;xsd:element name="item" minOccurs="0" maxOccurs="unbounded">
        &lt;xsd:complexType>
          &lt;xsd:sequence>
            &lt;xsd:element name="productName" type="xsd:string"/>
            &lt;xsd:element name="quantity">
              &lt;xsd:simpleType>
                &lt;xsd:restriction base="xsd:positiveInteger">
                  &lt;xsd:maxExclusive value="100"/>
                &lt;/xsd:restriction>
              &lt;/xsd:simpleType>
            &lt;/xsd:element>
            &lt;xsd:element name="USPrice"  type="xsd:decimal"/>
            &lt;xsd:element ref="comment"   minOccurs="0"/>
            &lt;xsd:element name="shipDate" type="xsd:date" minOccurs="0"/>
          &lt;/xsd:sequence>
          &lt;xsd:attribute name="partNum" type="SKU" use="required"/>
        &lt;/xsd:complexType>
      &lt;/xsd:element>
    &lt;/xsd:sequence>
  &lt;/xsd:complexType>

  &lt;!-- Stock Keeping Unit, a code for identifying products -->
  &lt;xsd:simpleType name="SKU">
    &lt;xsd:restriction base="xsd:string">
      &lt;xsd:pattern value="\d{3}-[A-Z]{2}"/>
    &lt;/xsd:restriction>
  &lt;/xsd:simpleType>

&lt;/xsd:schema>
    </example>

    <p>A likely one-to-one translation of that into a tDOM schema
    definition script would be:</p>

    <example>
tdom::schema schema      
schema define {

    # Purchase order schema for Example.com.
    # Copyright 2000 Example.com. All rights reserved.

    defelement purchaseOrder {ref PurchaseOrderType}

    foreach elm {comment name street city state product} {
        defelement $elm text
    }

    defpattern PurchaseOrderType {
        element shipTo ! {ref USAddress}
        element billTo ! {ref USAddress}
        element comment ?
        element items
        attribute orderDate date
    }

    defpattern USAddress {
        element name
        element street
        element city
        element state
        element zip ! {text number}
        attribute country ! {fixed "US"}
    }

    defelement items {
        element item * {
            element product
            element quantity ! {text integer}
            element USPrice ! {text number}
            element comment
            element shipDate ? {text date}
            attribute partNum ! {pattern "^\d{3}-[A-Z]{2}$"}
        }
    }
}
      
    </example>

    <p>The RELAX NG Tutorial
    (<url>http://relaxng.org/tutorial-20011203.html</url>) starts with
    this example:</p>

    <example>
Consider a simple XML representation of an email address book:

&lt;addressBook>
  &lt;card>
    &lt;name>John Smith&lt;/name>
    &lt;email>js@example.com&lt;/email>
  &lt;/card>
  &lt;card>
    &lt;name>Fred Bloggs&lt;/name>
    &lt;email>fb@example.net&lt;/email>
  &lt;/card>
&lt;/addressBook>

The DTD would be as follows:

&lt;!DOCTYPE addressBook [
&lt;!ELEMENT addressBook (card*)>
&lt;!ELEMENT card (name, email)>
&lt;!ELEMENT name (#PCDATA)>
&lt;!ELEMENT email (#PCDATA)>
]>

A RELAX NG pattern for this could be written as follows:

&lt;element name="addressBook" xmlns="http://relaxng.org/ns/structure/1.0">
  &lt;zeroOrMore>
    &lt;element name="card">
      &lt;element name="name">
        &lt;text/>
      &lt;/element>
      &lt;element name="email">
        &lt;text/>
      &lt;/element>
    &lt;/element>
  &lt;/zeroOrMore>
&lt;/element>
      
    </example>

    <p>This schema definition script will do the same:</p>

    <example>
tdom::schema schema      
schema define {
    defelement addressBook {
        element card *
    }
    defelement card {
        element name
        element email
    }
    foreach e {name email} {
        defelement $e text
    }
}
      
    </example>
</section>

<keywords>
    <keyword>Validation</keyword>
    <keyword>Postvalidation</keyword>
    <keyword>DOM</keyword>
    <keyword>SAX</keyword>
</keywords>
</manpage>
