E0151: Markup outside a .vuka.html file

Markup is written in .vuka.html files, and only there: a .vuka.html file declares one struct in its <script lang="go"> and its markup below renders it. .vuka and .go files are logic — services, models, helpers, main — and hold no markup. A .vuka.html file's script holds none either: its markup follows </script>.

The compiler still lowers markup the way it lowered JSX in a .vuka file; it is the place it is written that is one. A function that returned markup becomes a component: a .vuka.html file whose struct's exported fields are the function's parameters, used as a tag.

Wrong

// card.vuka
package components

type Card struct {
	Title string
}

func (c Card) View() ui.Node {
	return <h2>{c.Title}</h2>
}

Right

<!-- card.vuka.html -->
<script lang="go">
package components

type Card struct {
	Title string
}
</script>

<h2>{Title}</h2>