Private Use are of font

The HTML validator gave me a warning that the "Private Use Area" of a font
should not be used in a document.   But in this case the HTML used was

<span style="font-family:MZ-Limelight;">B&#x266D;&#xE871;7</span>

where the font in question is embedded with the CSS:

@font-face 

{

    font-family: MZ-Limelight;

    src: url('_font-embed/MZ-Limelight-Regular.otf');

    src: url('_font-embed/MZ-Limelight-Regular.woff');

}

 

And this font has precisely the correct private use glyph.  I wonder if the
warning could be tempered for the case where an embedded font is referenced?

 

David Webber
Mozart Music Software
https://www.mozart.co.uk