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HTML validation

Open W3C HTML validator. Copy and paste following HTML code to the validator.

<!doctype html>

<html>
<head>
  <meta charset="utf-8">

  <title>I'm very cool title for a cool page</title>

</head>

<body>
<section>
  <button>A</button>
  <button>B</button>
  <button>C</button>
  <button>D</button>
  <button hidden>E</button>
</section>
<section hidden>
  <h1>Hello H1!</h1>
  <h2>Hello H2!</h2>
  <h3>Hello H3!</h3>
</section>
<comment>
  <!--I'm a comment-->
</comment>
<dialog-block>
  <dialog open>always open</dialog>
</dialog-block>
</body>
</html>

Answer questions below based on the validator feedback.

How many errors and warnings does the validator give?

What’s wrong in the lines 1-3?

What’s the second warning about?

What’s wrong in the line 24?

What element is suggested by the validator inside a section if a heading is not needed?

Posting submission...