7.9.14 base.text.u Underlined text
To underline text use the <u> element. Not recommended since underlines are
used by web browsers to style hyperlinks.
Example
This line of text will render as underlined
Markup: base/text/text-u.twig
<u class="{{modifier_class}}">This line of text will render as underlined</u>
Source:
base/text/_text.scss, line 228