c3d2-web/html5-syntax/web-forms.rng

<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0" xmlns="http://relaxng.org/ns/structure/1.0">
  <!-- ##################################################################### -->
  <define name="common-form.attrs">
    <a:documentation> RELAX NG Schema for HTML 5: Web Forms 1.0 markup                  #</a:documentation>
    <!-- ##################################################################### -->
    <a:documentation>Shared attributes for form controls</a:documentation>
    <interleave>
      <optional>
        <ref name="common-form.attrs.name"/>
      </optional>
      <optional>
        <ref name="common-form.attrs.disabled"/>
      </optional>
    </interleave>
  </define>
  <define name="common-form.attrs.name">
    <attribute name="name">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT should this be restricted somehow? No & and = perhaps? -->
    </attribute>
  </define>
  <define name="common-form.attrs.disabled">
    <attribute name="disabled">
      <choice>
        <value type="string">disabled</value>
        <value type="string"/>
      </choice>
    </attribute>
  </define>
  <define name="shared-form.attrs.readonly">
    <attribute name="readonly">
      <choice>
        <value type="string">readonly</value>
        <value type="string"/>
      </choice>
    </attribute>
  </define>
  <define name="shared-form.attrs.maxlength">
    <attribute name="maxlength">
      <ref name="common.data.integer.positive"/>
      <!-- REVISIT should this be non-negative? -->
    </attribute>
  </define>
  <define name="shared-form.attrs.size">
    <attribute name="size">
      <ref name="common.data.integer.positive"/>
    </attribute>
  </define>
  <!-- REVISIT tabindex goes in common.attrs -->
  <define name="input.attrs.checked">
    <a:documentation>Shared attributes for &lt;input&gt;</a:documentation>
    <attribute name="checked">
      <choice>
        <value type="string">checked</value>
        <value type="string"/>
      </choice>
    </attribute>
  </define>
  <define name="input.text.elem">
    <a:documentation>Text Field: &lt;input type='text'&gt;</a:documentation>
    <element name="input">
      <ref name="input.text.attrs"/>
    </element>
  </define>
  <define name="input.text.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <optional>
        <ref name="input.text.attrs.type"/>
      </optional>
      <optional>
        <ref name="shared-form.attrs.maxlength"/>
      </optional>
      <optional>
        <ref name="shared-form.attrs.readonly"/>
      </optional>
      <optional>
        <ref name="shared-form.attrs.size"/>
      </optional>
      <optional>
        <ref name="input.text.attrs.value"/>
      </optional>
      <optional>
        <choice>
          <ref name="common.attrs.aria"/>
          <ref name="common.attrs.aria.implicit.input"/>
        </choice>
      </optional>
    </interleave>
  </define>
  <define name="input.text.attrs.type">
    <attribute name="type">
      <value type="string">text</value>
    </attribute>
  </define>
  <define name="input.text.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT "nominally" free of line breaks? -->
    </attribute>
  </define>
  <define name="input.elem">
    <ref name="input.text.elem"/>
  </define>
  <define name="input.password.elem">
    <a:documentation>Password Field: &lt;input type='password'&gt;</a:documentation>
    <element name="input">
      <ref name="input.password.attrs"/>
    </element>
  </define>
  <define name="input.password.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.password.attrs.type"/>
      <optional>
        <ref name="shared-form.attrs.maxlength"/>
      </optional>
      <optional>
        <ref name="shared-form.attrs.readonly"/>
      </optional>
      <optional>
        <ref name="shared-form.attrs.size"/>
      </optional>
      <optional>
        <ref name="input.password.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
  </define>
  <define name="input.password.attrs.type">
    <attribute name="type">
      <value type="string">password</value>
    </attribute>
  </define>
  <define name="input.password.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT "nominally" free of line breaks?			 -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.password.elem"/>
  </define>
  <define name="input.checkbox.elem">
    <a:documentation>Checkbox: &lt;input type='checkbox'&gt;</a:documentation>
    <element name="input">
      <ref name="input.checkbox.attrs"/>
    </element>
  </define>
  <define name="input.checkbox.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.checkbox.attrs.type"/>
      <optional>
        <ref name="input.attrs.checked"/>
      </optional>
      <optional>
        <ref name="input.checkbox.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
  </define>
  <define name="input.checkbox.attrs.type">
    <attribute name="type">
      <value type="string">checkbox</value>
    </attribute>
  </define>
  <define name="input.checkbox.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT require non-empty value? -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.checkbox.elem"/>
  </define>
  <define name="input.radio.elem">
    <a:documentation>Radiobutton: &lt;input type='radio'&gt;</a:documentation>
    <element name="input">
      <ref name="input.radio.attrs"/>
    </element>
  </define>
  <define name="input.radio.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.radio.attrs.type"/>
      <optional>
        <ref name="input.attrs.checked"/>
      </optional>
      <optional>
        <ref name="input.radio.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
  </define>
  <define name="input.radio.attrs.type">
    <attribute name="type">
      <value type="string">radio</value>
    </attribute>
  </define>
  <define name="input.radio.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT require non-empty value? -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.radio.elem"/>
  </define>
  <define name="input.button.elem">
    <a:documentation>Scripting Hook Button: &lt;input type='button'&gt;</a:documentation>
    <element name="input">
      <ref name="input.button.attrs"/>
    </element>
  </define>
  <define name="input.button.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.button.attrs.type"/>
      <optional>
        <ref name="input.button.attrs.value"/>
      </optional>
      <optional>
        <choice>
          <ref name="common.attrs.aria"/>
          <ref name="common.attrs.aria.implicit.button"/>
        </choice>
      </optional>
    </interleave>
  </define>
  <define name="input.button.attrs.type">
    <attribute name="type">
      <value type="string">button</value>
    </attribute>
  </define>
  <define name="input.button.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT require non-empty value? -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.button.elem"/>
  </define>
  <!-- REVISIT should this be enabled by a scripting module only? -->
  <define name="input.submit.elem">
    <a:documentation>Submit Button: &lt;input type='submit'&gt;</a:documentation>
    <element name="input">
      <ref name="input.submit.attrs"/>
    </element>
  </define>
  <define name="input.submit.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.submit.attrs.type"/>
      <optional>
        <ref name="input.submit.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.button"/>
      </optional>
    </interleave>
  </define>
  <define name="input.submit.attrs.type">
    <attribute name="type">
      <value type="string">submit</value>
    </attribute>
  </define>
  <define name="input.submit.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT require non-empty value? -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.submit.elem"/>
  </define>
  <define name="input.reset.elem">
    <a:documentation>Reset Button: &lt;input type='reset'&gt;</a:documentation>
    <element name="input">
      <ref name="input.reset.attrs"/>
    </element>
  </define>
  <define name="input.reset.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.reset.attrs.type"/>
      <optional>
        <ref name="input.reset.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.button"/>
      </optional>
    </interleave>
  </define>
  <define name="input.reset.attrs.type">
    <attribute name="type">
      <value type="string">reset</value>
    </attribute>
  </define>
  <define name="input.reset.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
      <!-- REVISIT require non-empty value? -->
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.reset.elem"/>
  </define>
  <!-- REVISIT does reset make sense outside a form? -->
  <define name="input.file.elem">
    <a:documentation>File Upload: &lt;input type='file'&gt;</a:documentation>
    <element name="input">
      <ref name="input.file.attrs"/>
    </element>
  </define>
  <define name="input.file.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.file.attrs.type"/>
      <optional>
        <ref name="input.file.attrs.accept"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
  </define>
  <define name="input.file.attrs.type">
    <attribute name="type">
      <value type="string">file</value>
    </attribute>
  </define>
  <define name="input.file.attrs.accept">
    <attribute name="accept">
      <ref name="form.data.mimetypelist"/>
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.file.elem"/>
  </define>
  <define name="input.hidden.elem">
    <a:documentation>Hidden String: &lt;input type='hidden'&gt;</a:documentation>
    <element name="input">
      <ref name="input.hidden.attrs"/>
    </element>
  </define>
  <define name="input.hidden.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.hidden.attrs.type"/>
      <optional>
        <ref name="input.hidden.attrs.value"/>
      </optional>
    </interleave>
  </define>
  <define name="input.hidden.attrs.type">
    <attribute name="type">
      <value type="string">hidden</value>
    </attribute>
  </define>
  <define name="input.hidden.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.hidden.elem"/>
  </define>
  <define name="input.image.elem">
    <a:documentation>Image Submit Button: &lt;input type='image'&gt;</a:documentation>
    <element name="input">
      <ref name="input.image.attrs"/>
    </element>
  </define>
  <define name="input.image.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="input.image.attrs.type"/>
      <ref name="input.image.attrs.alt"/>
      <optional>
        <ref name="input.image.attrs.src"/>
      </optional>
      <optional>
        <choice>
          <ref name="common.attrs.aria"/>
          <ref name="common.attrs.aria.implicit.button"/>
        </choice>
      </optional>
    </interleave>
  </define>
  <define name="input.image.attrs.type">
    <attribute name="type">
      <value type="string">image</value>
    </attribute>
  </define>
  <define name="input.image.attrs.alt">
    <attribute name="alt">
      <data type="string" datatypeLibrary=""/>
      <!-- XXX non-empty -->
    </attribute>
  </define>
  <define name="input.image.attrs.src">
    <attribute name="src">
      <ref name="common.data.uri"/>
    </attribute>
  </define>
  <define name="input.elem" combine="choice">
    <ref name="input.image.elem"/>
  </define>
  <define name="common.elem.phrasing" combine="choice">
    <ref name="input.elem"/>
  </define>
  <define name="textarea.elem">
    <a:documentation>Text Area: &lt;textarea&gt;</a:documentation>
    <element name="textarea">
      <interleave>
        <ref name="textarea.inner"/>
        <ref name="textarea.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="textarea.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <optional>
        <ref name="shared-form.attrs.readonly"/>
      </optional>
      <ref name="textarea.attrs.rows-and-cols-wf1"/>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
    <!-- FIXME onfocus, onblur, onselect,onchange -->
  </define>
  <!-- This is ugly. -->
  <define name="textarea.attrs.rows-and-cols-wf1">
    <ref name="textarea.attrs.rows-and-cols-wf1.inner"/>
  </define>
  <define name="textarea.attrs.rows-and-cols-wf1.inner">
    <interleave>
      <ref name="textarea.attrs.cols"/>
      <ref name="textarea.attrs.rows"/>
    </interleave>
  </define>
  <define name="textarea.attrs.cols">
    <attribute name="cols">
      <ref name="common.data.integer.positive"/>
    </attribute>
  </define>
  <define name="textarea.attrs.rows">
    <attribute name="rows">
      <ref name="common.data.integer.positive"/>
    </attribute>
  </define>
  <define name="textarea.inner">
    <text/>
  </define>
  <define name="common.elem.phrasing" combine="choice">
    <ref name="textarea.elem"/>
  </define>
  <!--
    Due to limitations with interleave, handling single/multiple selection
    enforcement in RELAX NG seems to be possible but really awkward.
    Tried it. Leaving it to Schematron.
  -->
  <define name="option.elem">
    <a:documentation>Select menu option: &lt;option selected&gt;</a:documentation>
    <element name="option">
      <interleave>
        <ref name="option.inner"/>
        <ref name="option.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="option.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <optional>
        <ref name="common-form.attrs.disabled"/>
      </optional>
      <optional>
        <ref name="option.attrs.selected"/>
      </optional>
      <optional>
        <ref name="option.attrs.label"/>
      </optional>
      <optional>
        <ref name="option.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.input"/>
      </optional>
    </interleave>
  </define>
  <define name="option.attrs.selected">
    <attribute name="selected">
      <choice>
        <value type="string">selected</value>
        <value type="string"/>
      </choice>
    </attribute>
  </define>
  <define name="option.attrs.label">
    <attribute name="label">
      <data type="string" datatypeLibrary=""/>
    </attribute>
  </define>
  <define name="option.attrs.value">
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
    </attribute>
  </define>
  <define name="option.inner">
    <text/>
  </define>
  <define name="optgroup.elem">
    <a:documentation>Option Group: &lt;optgroup&gt;</a:documentation>
    <element name="optgroup">
      <interleave>
        <ref name="optgroup.inner"/>
        <ref name="optgroup.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="optgroup.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="optgroup.attrs.label"/>
      <optional>
        <ref name="common-form.attrs.disabled"/>
      </optional>
    </interleave>
  </define>
  <define name="optgroup.attrs.label">
    <attribute name="label">
      <data type="string" datatypeLibrary=""/>
    </attribute>
  </define>
  <define name="optgroup.inner">
    <zeroOrMore>
      <ref name="option.elem"/>
    </zeroOrMore>
  </define>
  <define name="select.elem">
    <a:documentation>Selection Menu: &lt;select&gt;</a:documentation>
    <element name="select">
      <interleave>
        <ref name="select.inner"/>
        <ref name="select.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="select.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <optional>
        <ref name="select.attrs.size"/>
      </optional>
      <optional>
        <ref name="select.attrs.multiple"/>
      </optional>
    </interleave>
    <!-- FIXME onfocus, onblur, onchange -->
  </define>
  <define name="select.attrs.size">
    <attribute name="size">
      <ref name="common.data.integer.positive"/>
    </attribute>
  </define>
  <define name="select.attrs.multiple">
    <attribute name="multiple">
      <choice>
        <value type="string">multiple</value>
        <value type="string"/>
      </choice>
    </attribute>
  </define>
  <define name="select.inner">
    <interleave>
      <zeroOrMore>
        <ref name="optgroup.elem"/>
      </zeroOrMore>
      <zeroOrMore>
        <ref name="option.elem"/>
      </zeroOrMore>
    </interleave>
  </define>
  <define name="common.elem.phrasing" combine="choice">
    <ref name="select.elem"/>
  </define>
  <define name="button.attrs.value">
    <a:documentation>Shared Definitions for Complex Button</a:documentation>
    <attribute name="value">
      <data type="string" datatypeLibrary=""/>
    </attribute>
  </define>
  <define name="button.inner">
    <ref name="common.inner.phrasing"/>
  </define>
  <define name="button.submit.elem">
    <a:documentation>Complex Submit Button: &lt;button type='submit'&gt;</a:documentation>
    <element name="button">
      <interleave>
        <ref name="button.inner"/>
        <ref name="button.submit.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="button.submit.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <optional>
        <ref name="button.submit.attrs.type"/>
      </optional>
      <optional>
        <ref name="button.attrs.value"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.button"/>
      </optional>
    </interleave>
  </define>
  <define name="button.submit.attrs.type">
    <attribute name="type">
      <value type="string">submit</value>
    </attribute>
  </define>
  <define name="button.elem">
    <ref name="button.submit.elem"/>
  </define>
  <define name="button.reset.elem">
    <a:documentation>Complex Reset Button: &lt;button type='reset'&gt;</a:documentation>
    <element name="button">
      <interleave>
        <ref name="button.inner"/>
        <ref name="button.reset.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="button.reset.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="button.reset.attrs.type"/>
      <optional>
        <ref name="button.attrs.value"/>
      </optional>
      <optional>
        <!-- REVISIT I guess this still affects the DOM -->
        <ref name="common.attrs.aria.implicit.button"/>
      </optional>
    </interleave>
  </define>
  <define name="button.reset.attrs.type">
    <attribute name="type">
      <value type="string">reset</value>
    </attribute>
  </define>
  <define name="button.elem" combine="choice">
    <ref name="button.reset.elem"/>
  </define>
  <define name="button.button.elem">
    <a:documentation>Complex Push Button: &lt;button type='button'&gt;</a:documentation>
    <element name="button">
      <interleave>
        <ref name="button.inner"/>
        <ref name="button.button.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="button.button.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <ref name="common-form.attrs"/>
      <ref name="button.button.attrs.type"/>
      <optional>
        <ref name="button.attrs.value"/>
      </optional>
      <optional>
        <!-- REVISIT I guess this still affects the DOM -->
        <choice>
          <ref name="common.attrs.aria"/>
          <ref name="common.attrs.aria.implicit.button"/>
        </choice>
      </optional>
    </interleave>
  </define>
  <define name="button.button.attrs.type">
    <attribute name="type">
      <value type="string">button</value>
    </attribute>
  </define>
  <define name="button.elem" combine="choice">
    <ref name="button.button.elem"/>
  </define>
  <define name="common.elem.phrasing" combine="choice">
    <ref name="button.elem"/>
  </define>
  <define name="form.elem">
    <a:documentation>Form: &lt;form&gt;</a:documentation>
    <element name="form">
      <interleave>
        <ref name="form.inner"/>
        <ref name="form.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="form.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <optional>
        <ref name="form.attrs.action"/>
      </optional>
      <optional>
        <!-- REVISIT Should this be required anyway? -->
        <ref name="form.attrs.method"/>
      </optional>
      <optional>
        <ref name="form.attrs.enctype"/>
      </optional>
      <optional>
        <ref name="common-form.attrs.name"/>
      </optional>
      <optional>
        <ref name="form.attrs.accept-charset"/>
      </optional>
      <optional>
        <choice>
          <ref name="common.attrs.aria"/>
          <ref name="common.attrs.aria.implicit.region"/>
        </choice>
      </optional>
    </interleave>
  </define>
  <define name="form.attrs.action">
    <attribute name="action">
      <ref name="common.data.uri"/>
    </attribute>
  </define>
  <define name="form.attrs.method">
    <attribute name="method">
      <ref name="form.attrs.method.data"/>
    </attribute>
  </define>
  <define name="form.attrs.method.data">
    <choice>
      <value type="string">get</value>
      <value type="string">post</value>
    </choice>
  </define>
  <define name="form.attrs.enctype">
    <attribute name="enctype">
      <ref name="form.attrs.enctype.data"/>
    </attribute>
  </define>
  <define name="form.attrs.enctype.data">
    <choice>
      <value type="string">application/x-www-form-urlencoded</value>
      <value type="string">multipart/form-data</value>
    </choice>
  </define>
  <define name="form.attrs.accept-charset">
    <attribute name="accept-charset">
      <ref name="form.data.charsetlist"/>
    </attribute>
  </define>
  <define name="form.inner">
    <ref name="common.inner.flow"/>
  </define>
  <define name="common.elem.flow" combine="choice">
    <ref name="form.elem"/>
  </define>
  <define name="fieldset.elem">
    <a:documentation>Fieldset: &lt;fieldset&gt;</a:documentation>
    <element name="fieldset">
      <interleave>
        <ref name="fieldset.inner"/>
        <ref name="fieldset.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="fieldset.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <optional>
        <ref name="common.attrs.aria.implicit.group"/>
      </optional>
    </interleave>
  </define>
  <define name="fieldset.inner">
    <optional>
      <ref name="legend.elem"/>
    </optional>
    <!-- REVISIT should this be required? -->
    <ref name="common.inner.flow"/>
  </define>
  <define name="common.elem.flow" combine="choice">
    <ref name="fieldset.elem"/>
  </define>
  <define name="label.elem">
    <a:documentation>Label: &lt;label&gt;</a:documentation>
    <element name="label">
      <interleave>
        <ref name="label.inner"/>
        <ref name="label.attrs"/>
      </interleave>
    </element>
  </define>
  <define name="label.attrs">
    <interleave>
      <ref name="common.attrs"/>
      <optional>
        <ref name="label.attrs.for"/>
      </optional>
      <optional>
        <ref name="common.attrs.aria.implicit.region"/>
      </optional>
    </interleave>
  </define>
  <define name="label.attrs.for">
    <attribute name="for">
      <ref name="common.data.idref"/>
    </attribute>
  </define>
  <define name="label.inner">
    <ref name="common.inner.phrasing"/>
  </define>
  <!-- REVISIT making obvious guess -->
  <define name="common.elem.phrasing" combine="choice">
    <ref name="label.elem"/>
  </define>
</grammar>