JSFiddle - React, Tailwind, and code Playground

HTML

<div id="fixture">
    <h3>A</h3>
    <h3>B</h3>
    <h3>C</h3>
    <code>]</code>
</div>

<table id="tests">
    <thead><tr>
        <th>Selector</th>
        <th>Length</th>
    </tr></thead>
    <tbody>
        <tr><td>h3:not(:nth-child(2), :nth-child(3))</td></tr>
        <tr><td>h3:contains(]), code:contains(])</td></tr>
        <tr><td>*:not(kbd, code[title*='(parenthesized)'])</td></tr>
        <tr><td>#fixture:UndefinedPseudo *</td></tr>
    </tbody>
</table>

JavaScript

jQuery("#tests tbody td").each(function() {
    var selector = jQuery( this ).text(),
        $result = jQuery("<td>").appendTo( this.parentNode );
    try {
        $result.text( jQuery( selector ).length );
    } catch ( x ) {
        jQuery("<strong>").text( "ERR: " + ( x.message || x ) ).appendTo( $result );
    }
});