You could always URL-encode the "|".  But for me, your fragment validates when properly embedded :

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
   "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
   <link href="https://fonts.googleapis.com/css?family=Roboto|Roboto+Mono|Playfair+Display:700,900" rel="stylesheet">
   <title>I AM YOUR DOCUMENT TITLE REPLACE ME</title>
   <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
   <meta http-equiv="Content-Style-Type" content="text/css">
</head>
<body>
   <div>
   </div>
</body>
</html>

Philip Taylor
--------

Trucsweb.com wrote:
Hi,

  1. Error: Bad value https://fonts.googleapis.com/css?family=Roboto|Roboto+Mono|Playfair+Display:700,900 for attribute href on element link: Illegal character in query: | is not allowed.

    From line 36, column 5; to line 36, column 120

    t" />↩ <link href="https://fonts.googleapis.com/css?family=Roboto|Roboto+Mono|Playfair+Display:700,900" rel="stylesheet" />↩ <

It's may be the time for autorise |?

Tx