Binding selection value to an external input

I am trying to build a simple example of binding a vega-lite selection to an external input. Can anyone help me with that? I have a notebook here:

viewof date = htl.html<input type=text>

and in my spec,

params: [
      name: "brush",
      select: { type: "interval", encodings: ["x"] },
      value: { month_date: [1331110440000, 1350043886250] },
      bind: { element: viewof date }

That shows the selection in the chart, but not in the input. I would like a two-way binding with the input and the chart selection.

Thanks for any help.