It's sufficiently easy to brew a primitive single-line tooltip:
<span title="British Rail">BR</span>
But the method stops being useful with longer texts. How can I brew a multiline tooltip? Using "<br>" inside "<span>" is not possible. There is the "hover" CSS selector that can brew sophisticated and multiline tooltips, but I can't find a way to use it from wikitext.
Is there a way to brew a multiline tooltip from inside wikitext?