<optgroup>
Headings that divide a long list of options.
Inside a <select>, it groups <option> elements under a label that cannot be selected. One level only: the specification does not allow groups inside groups.
disabled switches off the whole group at once, which is useful when a set of options depends on another choice in the form.
<select name="etiqueta">
<optgroup label="Text">
<option>abbr</option>
<option>time</option>
</optgroup>
<optgroup label="Forms">
<option>meter</option>
<option>output</option>
</optgroup>
</select>