{{$size := get .Content "size"}}

<section>
    {{if $size}}
        {{html (fmt "<%s>" $size)}}
            {{copy .Page .Content "headline"}}
        {{html (fmt "</%s>" $size)}}
    {{else}}
        <h2>{{copy .Page .Content "headline"}}</h2>
    {{end}}

    {{html (copy .Page .Content "text")}}
</section>