code: private FilterUtils getFilterUtils(final Element ditavalRef) {
          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;
          return filterCache.computeIfAbsent(ditaval, this::getFilterUtils);
      }
docs: Read referenced DITAVAL and cache filter.