code: public static void setDocumentHelpers (JTextComponent comp, DocumentValidator validator,
                                             DocumentTransformer transformer)
      {
          setDocumentHelpers(comp.getDocument(), validator, transformer);
      }
docs: Set active Document helpers on the specified text component.  Changes will not and cannot be
  made (either via user inputs or direct method manipulation) unless the validator says that
  the changes are ok.
  
  @param validator if non-null, all changes are sent to this for approval.
  @param transformer if non-null, is queried to change the text after all changes are made.