code: @SuppressWarnings("JavaDoc")
      public static Multiset<String> getIdentifiersFrom(String mathml) {
          Multiset<String> list = HashMultiset.create();
          Pattern p = Pattern.compile("<((m:)?[mc][ion])(.*?)>(.{1,4}?)</\\1>", Pattern.DOTALL);
          Matcher m = p.matcher(mathml);
          while (m.find()) {
              String identifier = m.group(4);
              list.add(identifier);
          }
          return list;
      }
docs: Returns a list of unique identifiers from a MathML string.
  This function searches for all mi- or ci-tags within
  the string.
  
  @param mathml
  @return a list of unique identifiers. When no identifiers were
  found, an empty list will be returned.