The rt element marks the ruby text component of a ruby annotation.
rt = (normal-character-data & common.elem.phrasing*) & rt.attrs
rt.attrs = common.attrs & common.attrs.aria?
An rt element must have a start tag.
rt
An rt element's end tag may be omitted if the rt element is immediately followed by an rt or rp element, or if there is no more content in the parent element.
rp