code: @GwtIncompatible("java.io.File")
    public static VariableMap load(String filename) throws IOException {
      try {
        return fromBytes(Files.toByteArray(new File(filename)));
      } catch (ParseException e) {
        // Wrap parse exception for backwards compatibility.
        throw new IOException(e);
      }
    }
docs: Reads the variable map from a file written via {@link #save(String)}.