5. dtd

<dtd
  systemId = anyURI
  publicId = non empty token
/>

Use the DTD specified by this element to constrain the document.

Note that

the grammar specified this way is used and the DTD specified in the configuration file is ignored.

Example:

  <dtd publicId="-//W3C//DTD XHTML 1.0 Strict//EN" 
       systemId="dtd/xhtml1-strict.dtd" />

It possible to use both a schema or relaxng configuration element and a dtd configuration element but in this case, the dtd configuration element cannot be used to specify a content model. It may be used to specify a set of character entities.