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HTML Checking for Large Sites

Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.

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 -->

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Related W3C validator issues