code: private ExtensionsElement readExtensions(Location location, String documentation) {
      int start = reader.readInt(); // Range start.
      int end = start;
      if (reader.peekChar() != ';') {
        if (!"to".equals(reader.readWord())) throw reader.unexpected("expected ';' or 'to'");
        String s = reader.readWord(); // Range end.
        if (s.equals("max")) {
          end = Util.MAX_TAG_VALUE;
        } else {
          end = Integer.parseInt(s);
        }
      }
      reader.require(';');
      return new ExtensionsElement(location, documentation, start, end);
    }
docs: Reads extensions like "extensions 101;" or "extensions 101 to max;".