hugo-paper/layouts/shortcodes/collapse.html

{{ if .Get "content" }}
{{ if .Get "summary" }}
{{ else }}
{{ warnf "missing value for param 'summary': %s" .Position }}
{{ end }}
{{ else }}
{{ errorf "missing value for param 'content': %s" .Position }}
{{ end }}

<p>
  <details {{ if (eq (.Get "openByDefault") true) }}open=true{{ end }}>
    <summary markdown="span">{{ .Get "summary" | markdownify }}</summary>
    {{ .Get "content" | markdownify }}
  </details>
</p>