epubcheck does not accept a CSS :is pseudo-class #1289
Description
Consider the following content file:
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" xml:lang="en">
<head>
<title>CSS test for :is</title>
<style>
:is(h1,h2,h3,h4,h5,h6,a) abbr{border:none}
</style>
</head>
<body>
<p>This is a possible epubcheck bug...</p>
</body>
</html>
the epubcheck response is as follows:
Validating using EPUB version 3.3 rules.
ERROR(CSS-008): css-bug.epub/OPS/content_001.xhtml(5,13): An error occurred while parsing the CSS: Token "," not allowed here.
I believe the CSS :is(...) syntax is correct and epubcheck should accept it.
I have also created a small epub file encapsulating this content file, see https://www.dropbox.com/s/d3gwhyg9agjtazx/css-bug.epub?dl=0