[attr="double"] {
    background: url("/double/quoted/path");
}

[attr='single'] {
    background: url('/single/quoted/path');
}

[attr=no-quotes] {
    /* this url-token should stay unquoted */
    background: url(/unquoted/path);
}

[attr=\eescaped] {
}

div {
    width: 0\eestays-unquoted;
    --\eeunquoted: green;
    color: var(--\eeunquoted);
}