Limit tags when rendering @html

[jimafisk]

In Svelte, variables are normally rendered as plain text, but you can render HTML using syntax like {@html expression} see more details and demo. It would be nice to be able to optionally limit which tags are allowed when rendering, for example:

<script>
	let string = "<p><em>this</em> string contains<br> some <strong>HTML!!!</strong></p>";
</script>

<p>{@html[strong, em] string}</p>

Output should look like this:

<p>this string contains<br> some HTML!!!</p>