W3C don't validate Viewport

Question

W3C don't validate my viewport meta tag any idea why?

<title>DIDIx13</title>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no" /> 
<!-- Throws a warning "Consider avoiding viewport values that prevent users from resizing documents." -->
<meta name="keywords" content="DIDIx13" >
<meta name="description" content="I'm Darwin and welcome to my website" >

Answer 1

TL;DR

Remove "user-scalable=no" and now the validator is fully ok!

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I've found out the purpose of "user-scalable=no", thanks to this answer.

Actually "user-scalable=no" prevents the user from zooming. And it allows the browser to gain 300ms per click.

300ms per click? That's pretty damn good! I should let "user-scalable=no"

But this is no longer the case, according to efheng's answer.

<meta name="viewport" content="width=device-width"> is enough to remove 300ms delay.

Answer 2

Pay attention that any -scale property also triggers that warning

Therefore you should remove all of the following properties, if existent

• user-scalable
• initial-scale
• maximum-scale
• minimum-scale