25. schema

<schema>
  Content: location | noNamespaceLocation | (location noNamespaceLocation)
</schema>

<location>
  Content: list of anyURI pairs
</location>

<noNamespaceLocation>
  Content: anyURI
</noNamespaceLocation>

Use the W3C XML Schema specified by this element to constrain the document.

The content of child element location is identical to the one of standard attribute xsi:schemaLocation. The content of child element noNamespaceLocation is identical to the one of standard attribute xsi:noNamespaceSchemaLocation.

Note that

the grammar specified this way is used and the W3C XML Schema specified in the configuration file is ignored.

Example:

<schema>
  <location>http://www.w3.org/1999/xhtml
            xsd/5.0/xhtml5.xsd</location>
</schema>

Validating W3C XML Schemas

If your configuration allows to edit W3C XML Schemas, you'll typically specify:

<schema>
  <location>http://www.w3.org/2001/XMLSchema
            xsd/XMLSchema.xsd</location>
</schema>

where xsd/XMLSchema.xsd is a copy of the XML Schema for XML Schemas.

However, it is also possible to validate the document being edited using XXE's built-in schema validator. This kind of validation is more comprehensive than the one performed by the XML Schema for XML Schema alone. This is achieved by referencing the "xxe-schema-for-schema" dummy URI:

<schema>
  <location>http://www.w3.org/2001/XMLSchema
            xxe-schema-for-schema</location>
</schema>