When dealing with this particular HTML code, there is a feature where a list item includes options such as all, a, b, c, and d. If the user selects 'All', it should restrict them from choosing any other items. However, if they do not choose 'All', they should be able to select multiple items from the list.
<html>
<body>
<select id="mySelect" size="5" multiple="select-multiple">
<option>All</option>
<option>a</option>
<option>b</option>
<option>c</option>
<option>d</option>
</select>
<button onclick="alert(mySelect.multiple);">Multiple</button>
</body>
</html>