docs: private FilterUtils getFilterUtils(final Element ditavalRef) {
          if (ditavalRef.getAttribute(ATTRIBUTE_NAME_HREF).isEmpty()) {
              return null;
          }
          final URI href = toURI(ditavalRef.getAttribute(ATTRIBUTE_NAME_HREF));
          final URI tmp = currentFile.resolve(href);
          final FileInfo fi = job.getFileInfo(tmp);
          final URI ditaval = fi.src;
          FilterUtils f = filterCache.get(ditaval);
          if (f == null) {
              ditaValReader.filterReset();
              logger.info("Reading " + ditaval);
              ditaValReader.read(ditaval);
              Map<FilterUtils.FilterKey, FilterUtils.Action> filterMap = ditaValReader.getFilterMap();
              f = new FilterUtils(filterMap, ditaValReader.getForegroundConflictColor(), ditaValReader.getBackgroundConflictColor());
              f.setLogger(logger);
              filterCache.put(ditaval, f);
          }
          return f;
      }