Settings: Override the user-scalable viewport meta tag so it doesn't prevent the user from scaling the page

Example:

<!doctype html>
<html lang="en">
 <head>
   <meta name="viewport" content="width=device-width, user-scalable=no">
   ...
 </head>
 <body>...</body>
</html>

Add an option on the settings page to override this if it's included in the theme. It is straightforward to resolve this issue - simply remove the user-scalable attribute entirely.

We might consider setting the initial-scale:

<meta name="viewport" content="width=device-width, initial-scale=1">

equalizedigital / accessibility-checker

Settings: Override the user-scalable viewport meta tag so it doesn't prevent the user from scaling the page #589