EPUBCheck does not accept class selector in CSS :has pseudo-class #1618

Consider the following CSS syntax using the :has and :not pseudo-classes:

header :has(h1.header.chapter) {
  margin-top: 10px;
}

header :has(h1.header) {
  margin-top: 10px;
}

header :has(h1) {
  margin-top: 10px;
}

header :has(.header) {
  margin-top: 10px;
}

header :not(.header) {
  margin-top: 10px;
}

EPUBCheck v5.2.1 reports:

Validating using EPUB version 3.3 rules.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(1,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(1,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(5,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(5,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(9,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(9,13): An error occurred while parsing the CSS: Token "h1" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(13,13): An error occurred while parsing the CSS: Token ".header" not allowed here.
ERROR(CSS-008): css_has_class_test.epub/OEBPS/css_has_test.css(13,13): An error occurred while parsing the CSS: Token ".header" not allowed here.

The above CSS syntax is valid and EPUBCheck should accept it. It appears errors are reported for class selectors used in the :has pseudo-class. A class selector in the :not pseudo-class is accepted.

I have created a test EPUB file, which includes the CSS pattern above. Please see: https://www.dropbox.com/scl/fi/urum4me6egoda1g31bhfv/css_has_class_test.epub?rlkey=8ly58gasqpuq87bpfu42nfqtq&st=isyiymvu&dl=0