css/css-syntax/unclosed-constructs.html

<!doctype html>
<title>Unclosed Constructs Are Valid</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<meta name="author" title="Tab Atkins-Bittner">
<link rel=help href="https://drafts.csswg.org/css-syntax/#rule-defs">

<!--
Tests that unclosed constructs are valid and match grammars,
because grammar-matching only sees the "block",
not the opening/closing characters themselves.
-->

<script>

function validSelector(str) {
    try {
        document.querySelector(str);
        return true;
    } catch(e) {
        return false;
    }
}
function shouldBeValid(str) {
    test(()=>{
        assert_true(validSelector(str));
    }, `"${str}" is a valid selector`)
}

shouldBeValid("[foo]");
shouldBeValid("[foo");
shouldBeValid(":nth-child(1)");
shouldBeValid(":nth-child(1");

</script>