Testing jQuery.after

HTML

<table>
  <tbody><tr id="itemsHeader"><th>This is a header</th></tr></tbody>
</table>

CSS

table {
    width: 70%;
    margin: auto;
    margin-top: 5px;
}

table, td, th {
    border: black solid 1px;
    padding: 2px;
}

th {
    font-weight: bold;
    text-align: center;
}

JavaScript

$('#itemsHeader').after(
    "<tr><td>a</td></tr>",
    "<tr><td>b</td></tr>"
);