If you click the check box DTD Validation then the validator will attempt to load and validate with the DTD, as well as any other schema processing.
Hint: If the SYSTEM identifier for DTD is at a remote site, please note that retrieving the DTD can add quite a few seconds to validation.
Hint: The default directory for DTDs is the schema directory. If you need to use a DTD, put it in the schema directory and just give the file name (no path needed) in the SYSTEM identifier of the document type declaration on your data:
<!DOCTYPE mydoc SYSTEM "x.dtd">
To save these defaults between sessions, press the Save button. To return to the validator using these settings, press OK