The spoiler syntax (
>! …) produces this HTML:
<blockquote class="spoiler"> <p>…</p> </blockquote>
However, spoilers are not (necessarily) quotes. The
blockquote element must only be used for "content that is quoted from another source".
As HTML5 provides no other appropriate element for this purpose, a
div element should be used instead:
<div class="spoiler"> <p>…</p> </div>