code: private void checkForbiddenTag(IfdTags metadata, String tagName, String ext) {
      int tagid = TiffTags.getTagId(tagName);
      if (metadata.containsTagId(tagid)) {
        validation.addErrorLoc("Forbidden tag for TiffEP found " + tagName, ext);
      }
    }
docs: Check a forbidden tag is not present.
  
  @param metadata the metadata
  @param tagName the tag name
  @param ext string extension