HTML Checking for Large Sites

Rocket Validator automatically checks your pages on the W3C Validator.

A document must not include more than one visible “main” element.

There can only be one visible <main> element in a document. If more are needed (for example for switching between them with JavaScript), only one can be visible, the others should be hidden toggling the hidden attribute.

Example of 2 main elements, where only one is visible:

  <h1>Active main element</h1>
  <!-- content -->

<main hidden>
  <h1>Hidden main element</h1>
  <!-- content -->

Learn more:

Related W3C validator issues

25,000 HTML checks per month. Is that enough for your site?

Save time using our automated web checker. Let our crawler check your web pages on the W3C Validator.