In XSD how do I allow only whitespace in an element's content?

Question

I am writing the XSD for an element that has no content, only attributes, which seems fairly straightforward:

  <xs:complexType name="ViewElement">
    <xs:attribute name="Name" type="xs:string" use="required"/>
  </xs:complexType>
  <xs:element name="VIEW" type="ViewElement" minOccurs="0" maxOccurs="unbounded"/>

If the XML contains

<VIEW Name='V_UP'></VIEW>

or

<VIEW Name='V_UP'/>

it works fine. But if the XML contains

<VIEW Name='V_UP'>
</VIEW>

I get

The element cannot contain white space. Content model is empty.

I want to allow the authors of the XML the flexibility to write the XML this way, but I can't work out how to allow content, but only whitespace content. Any suggestions?

Answer 1

You can use a xsd:whiteSpace facet with value="collapse" and require a length of 0:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="OnlyWhiteSpaceElement">
    <xs:simpleType>
      <xs:restriction base="xs:string">
        <xs:whiteSpace value="collapse"/>
        <xs:length value="0"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:element>
</xs:schema>

---

Update 1: OP would like to add attributes to OnlyWhiteSpaceElement

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="OnlyWhiteSpaceElement">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="OnlyWhiteSpaceType">
          <xs:attribute name="Name" type="xs:string" use="required"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

  <xs:simpleType name="OnlyWhiteSpaceType">
    <xs:restriction base="xs:string">
      <xs:whiteSpace value="collapse"/>
      <xs:length value="0"/>
    </xs:restriction> 
  </xs:simpleType> 
</xs:schema>

See also: Restrict complexType with attributes in XSD?

---

Update 2: OP would like to reuse the currently anonymous complex type. Let's defined a named type and refactor the names being used...

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="OnlyWhiteSpaceElement" type="OnlyWhiteSpaceType"/>

  <xs:complexType name="OnlyWhiteSpaceType">
    <xs:simpleContent>
      <xs:extension base="OnlyWhiteSpaceContentType">
        <xs:attribute name="Name" type="xs:string" use="required"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>

  <xs:simpleType name="OnlyWhiteSpaceContentType">
    <xs:restriction base="xs:string">
      <xs:whiteSpace value="collapse"/>
      <xs:length value="0"/>
    </xs:restriction> 
  </xs:simpleType> 
</xs:schema>

---

Update 3: Be aware of XSD processor implementation differences regarding xs:whiteSpace value="collapse".