The answer is in the following paragraphs from the Struts Validator Guide.
An alternative approach is to use the action mapping path attribute. In this case, you extend the ValidatorActionForm instead of the ValidatorForm. The ValidatorActionForm uses the action element's path attribute from the Struts configuration which should match the form element's name attribute in the Validator configuration.
Then a separate action mapping can be defined for each page in a multi-page form, and the validation form can be associated with the action rather than a page number (as shown in the example of a multi-page form in the validator example).