Here's a case when multiple roots throws an error:

```js
var html = require('nanohtml')

var nums = [10,20,30]

var el = html`

Hello planet

${nums.map(n =>
html``
)}
`
document.body.appendChild(el)
```

Updating nanohtml's `createFragment` to look something like this solves the problem:

```js
function createFragment (nodes) {
var fragment = document.createDocumentFragment()
for (var i = 0; i < nodes.length; i++) {
if (typeof nodes[i] === 'string') nodes[i] = document.createTextNode(nodes[i])

if (Array.isArray(nodes[i])) {
for (var n=0; n < nodes[i].length; n++) {
fragment.appendChild(nodes[i][n])
}
}
else {
fragment.appendChild(nodes[i])
}
}
return fragment
}
```