Using AMP to display a dropdown showing options for Results per Page

results_per_page.amp.html

<!--
Expect back-end src to respond with a results_per_page array of objects

{
  "items": {
    "results_per_page" :[{
      "value": "10",
      "text": "10",
      "selected": true
    },{
      "value": "50",
      "text": "50",
      "selected": false
    },{
      "value": "100",
      "text": "100",
      "selected": false
    },{
      "value": "all",
      "text": "All",
      "selected": false
    }]
  }
}
-->

<amp-list
  layout="flex-item"
  height="40"
  src="/filters.json.php"
  [src]="'/filters.json.php?<?=$initial?>">
  <template type="amp-mustache">
    {{current_items}}

    <select on="change:AMP.pushState({ filtering: { results_per_page: event.value }, product_list: { items: { loading: true } } })">
      <optgroup label="Results per Page">
        {{#results_per_page}}
          {{#selected}}
            <option value="{{value}}" selected>View {{text}}</option>
          {{/selected}}
          {{^selected}}
            <option value="{{value}}">View {{text}}</option>
          {{/selected}}
        {{/results_per_page}}
      </optgroup>
    </select>
  </template>
</amp-list>