code: static void append(Appendable outputBuf, SoyValue value, SoyNode node) {
      try {
        value.render(outputBuf);
      } catch (IOException e) {
        throw new RuntimeException(e);
      } catch (RenderException e) {
        throw e.addStackTraceElement(node);
      }
    }
docs: Helper to append a SoyValue to the output, propagating any exceptions.