Playground

Everything below runs in this page. The library is synchronous and has no dependencies, so the same code that renders on a server renders here.

What to try

• Put < or & in a piece of text and watch it come back escaped.
• Change a javascript: URL to https: and back. It is never an error, only a replacement.
• Delete a closing tag and see which error code comes back, and what the message says the browser would do.
• Give two elements the same id. The template check says nothing; check() finds it, because only a finished page can know.
• Swap aria-pressed for data-pressed and set it to false. One renders, one disappears — see attributes.
• Write a <style> block and style the markup. The preview renders in a shadow root, so it starts from the browser's own stylesheet rather than this site's, and nothing written there can reach the rest of this page.