One voice of the type scale, and the element it speaks through. The
interface roles (display to micro) are paragraphs; a role that names a
section is a heading's look, so give it h2 and that role's style.
Set type publishes one slot; it owns no state, messages, or bundles. The
level chooses the element: headings stay headings, body copy stays a
paragraph, and asides keep their small, blockquote, and code
semantics. Longform rhythm between unlike elements stays Prose's; this
is the single voice, wherever it stands.
One voice of the type scale in one call: its level, its words, a style
for its slot, and mixins beside the style. No upstream component stands
behind it.