Table of contents

Appendices

5.5 Any Element, Any Attribute

In previous sections we have seen several mechanisms for extending the content models of complex types. For example, a mixed content model can contain arbitrary character data in addition to elements, and for example, a content model can contain elements whose types are imported from external namespaces. However, these mechanisms provide very broad and very narrow controls respectively. The purpose of this section is to describe a flexible mechanism that enables content models to be extended by any elements and attributes belonging to specified namespaces.

To illustrate, consider a version of the quarterly report, 4Q99html.xml, in which we have embedded an XHTML representation of the XML parts data. The XHTML content appears as the content of the element htmlExample, and the default namespace is changed on the outermost XHTML element (table) so that all the XHTML elements belong to the XHTML namespace, http://www.w3.org/1999/xhtml:

NOTE: 

Quarterly Report with XHTML, 4Q99html.xml

<purchaseReport
  xmlns="http://www.example.com/Report"
  period="P3M" periodEnding="1999-12-31">

  <regions>
    <!-- part sales listed by zip code, data from 4Q99.xml -->
  </regions>

  <parts>
    <!-- part descriptions from 4Q99.xml -->
  </parts>

  <htmlExample>
    <table xmlns="http://www.w3.org/1999/xhtml"
           border="0" width="100%">
      <tr>
        <th align="left">Zip Code</th>
        <th align="left">Part Number</th>
        <th align="left">Quantity</th>
      </tr>
      <tr><td>95819</td><td> </td><td> </td></tr>
      <tr><td> </td><td>872-AA</td><td>1</td></tr>
      <tr><td> </td><td>926-AA</td><td>1</td></tr>
      <tr><td> </td><td>833-AA</td><td>1</td></tr>
      <tr><td> </td><td>455-BX</td><td>1</td></tr>
      <tr><td>63143</td><td> </td><td> </td></tr>
      <tr><td> </td><td>455-BX</td><td>4</td></tr>
    </table>
  </htmlExample>

</purchaseReport>

ref32To permit the appearance of XHTML in the instance document we modify the report schema by declaring a new element htmlExample whose content is defined by the any element. In general, an any element specifies that any well-formed XML is permissible in a type's content model. In the example, we require the XML to belong to the namespace http://www.w3.org/1999/xhtml, in other words, it should be XHTML. The example also requires there to be at least one element present from this namespace, as indicated by the values of minOccurs and maxOccurs:

NOTE: 

Modification to purchaseReport Declaration to Allow XHTML in Instance

<element name="purchaseReport">
  <complexType>
    <sequence>
      <element name="regions" type="r:RegionsType"/>
      <element name="parts"   type="r:PartsType"/>
      <element name="htmlExample">
        <complexType>
          <sequence>
            <any namespace="http://www.w3.org/1999/xhtml"
                 minOccurs="1" maxOccurs="unbounded"
                 processContents="skip"/>
          </sequence>
        </complexType>
      </element>
    </sequence>
    <attribute name="period"       type="duration"/>
    <attribute name="periodEnding" type="date"/>
  </complexType>
</element>

ref33The modification permits some well-formed XML belonging to the namespace http://www.w3.org/1999/xhtml to appear inside the htmlExample element. Therefore 4Q99html.xml is permissible because there is one element which (with its children) is well-formed, the element appears inside the appropriate element (htmlExample), and the instance document asserts that the element and its content belongs to the required namespace. However, the XHTML may not actually be valid because nothing in 4Q99html.xml by itself can provide that guarantee. If such a guarantee is required, the value of the processContents attribute should be set to strict (the default value). In this case, an XML processor is obliged to obtain the schema associated with the required namespace, and validate the XHTML appearing within the htmlExample element.

textTypeIn another example, we define a text type which is similar to the text type defined in XML Schema's introductory type library (see also [Type Libraries]), and is suitable for internationalized human-readable text. The text type allows an unrestricted mixture of character content and element content from any namespace, for example Ruby annotations, along with an optional xml:lang attribute. The lax value of the processContents attribute instructs an XML processor to validate the element content on a can-do basis: It will validate elements and attributes for which it can obtain schema information, but it will not signal errors for those it cannot obtain any schema information.

NOTE: 

Text Type

<xsd:complexType name="text">
  <xsd:complexContent mixed="true">
    <xsd:restriction base="xsd:anyType">
      <xsd:sequence>
        <xsd:any processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
      </xsd:sequence>
      <xsd:attribute ref="xml:lang"/>
    </xsd:restriction>
  </xsd:complexContent>
</xsd:complexType>

ref34Namespaces may be used to permit and forbid element content in various ways depending upon the value of the namespace attribute, as shown in Table 4:

ref35In addition to the any element which enables element content according to namespaces, there is a corresponding anyAttribute element which enables attributes to appear in elements. For example, we can permit any XHTML attribute to appear as part of the htmlExample element by adding anyAttribute to its declaration:

NOTE: 

Modification to htmlExample Declaration to Allow XHTML Attributes

<element name="htmlExample">
  <complexType>
    <sequence>
      <any namespace="http://www.w3.org/1999/xhtml"
           minOccurs="1" maxOccurs="unbounded"
           processContents="skip"/>
    </sequence>
    <anyAttribute namespace="http://www.w3.org/1999/xhtml"/>
  </complexType>
</element>

This declaration permits an XHTML attribute, say href, to appear in the htmlExample element. For example:

NOTE: 

An XHTML attribute in the htmlExample Element

....
  <htmlExample xmlns:h="http://www.w3.org/1999/xhtml"
               h:href="http://www.example.com/reports/4Q99.html">
    <!-- XHTML markup here -->
  </htmlExample>
....

The namespace attribute in an anyAttribute element can be set to any of the values listed in Table 4 for the any element, and anyAttribute can be specified with a processContents attribute. In contrast to an any element, anyAttribute cannot constrain the number of attributes that may appear in an element.