Consider this sample code, which accidentally omits a closing tag.

```js
import htm from 'https://unpkg.com/htm?module'
const h = (type, props, ...children) => ({type, props, children});
const html = htm.bind(h)

console.log(JSON.stringify(html`

Hello, world!`));
```

In this case, the user intended to include a closing tag `

`, and so the user's desired logged result is `{"type":"h1","props":null,"children":["Hello, world!"]}`

Actual: `["h1","Hello, world!"]` The element name is incorrectly handled as a text node.

Expected: Throw an exception.

Start by running the provided tagged-template sample with the htm runtime and reproduce how the missing is handled. Trace the parser path for an unclosed tag; done means the sample throws an exception instead of treating the element name as a text node, while valid tags continue to produce the expected object.

Written by the indexing model from the issue text.