docs: public void record(final String name,
                             final long value,
                             final String xtratag) {
      buf.setLength(0);
      buf.append(prefix).append(".")
         .append(name)
         .append(' ')
         .append(System.currentTimeMillis() / 1000)
         .append(' ')
         .append(value);
  
      if (xtratag != null) {
        if (xtratag.indexOf('=') != xtratag.lastIndexOf('=')) {
          throw new IllegalArgumentException("invalid xtratag: " + xtratag
              + " (multiple '=' signs), name=" + name + ", value=" + value);
        } else if (xtratag.indexOf('=') < 0) {
          throw new IllegalArgumentException("invalid xtratag: " + xtratag
              + " (missing '=' signs), name=" + name + ", value=" + value);
        }
        buf.append(' ').append(xtratag);
      }
  
      if (extratags != null) {
        for (final Map.Entry<String, String> entry : extratags.entrySet()) {
          buf.append(' ').append(entry.getKey())
             .append('=').append(entry.getValue());
        }
      }
      buf.append('\n');
      emit(buf.toString());
    }