{{ $uniq := .Inner | htmlEscape | md5 | lower }}
{{ $template := printf "template-%s" $uniq }}
{{ $string := replace "<script>(function() { ShadyCSS.prepareTemplate(template%s, 'demo-elem%s'); var script = template%s.content.querySelector('script'); if (script) { script.textContent = `(function() { var demo = document.querySelector('demo-elem%s').shadowRoot; ${script.textContent} })()` } class DemoElem extends HTMLElement { connectedCallback() { ShadyCSS.styleElement(this); this.attachShadow({mode: 'open'}); this.shadowRoot.appendChild(template%s.content.cloneNode(true)); } } customElements.define('demo-elem%s', DemoElem); })();</script>" "%s" $uniq }}
<div class="demo-container">
  {{ if .Get "caption" }}
  <figure role="group" aria-labelledby="caption-{{ $uniq }}">
  {{ end }}
      <demo-elem{{ $uniq }} class="demo" id="demo-{{ $uniq }}"></demo-elem{{ $uniq }}>
      {{ if .Get "caption" }}
          <figcaption id="caption-{{ $uniq }}">{{ .Get "caption" | markdownify }}</figcaption>
      {{ end }}
  {{ if .Get "caption" }}
  </figure>
  {{ end }}
  <template id="template{{ $uniq }}">
      {{ .Inner | safeHTML }}
  </template>
  {{ $string | safeHTML }}
</div>