code: public static boolean keepDoc(JCas jCas) {
          String lang = jCas.getDocumentLanguage();
          if (lang.equals("x-unspecified")) {
              LOG.warn("document language needed to decide whether to keepDoc(), but document language is not set, pmId"
                      + getHeaderDocId(jCas));
          }
          if (!(lang.equals("en") || lang.equals("x-unspecified")) || //
                  exists(jCas, TooFewTokensPerPage.class) || //
                  exists(jCas, TooManyOOV.class)) {
              return false;
          }
          return true;
      }
docs: Whether this document should be kept for analysis, based on:
  <ul>
  <li>language == en</li>
  <li>OOV < 0.4 (see {@link TooMuchOOVFilterAnnotator})</li>
  <li>Enough tokens per page (see {@link TooFewTokensFilterAnnotator})</li>
  </ul>