HTML/CSS/Form Attributes/multiple
"multiple" sets whether "option" elements can be multiple selected
<source lang="html4strict">
<HTML> <BODY> <body onUnload="document.forms[0].reset()">
<form name="form1" method="post" action=""> <select name="Chapters" multiple> <option>Chapter 1</option> <option>Chapter 2</option> <option>Chapter 3</option> <option>Chapter 4</option> <option>Chapter 5</option> <option>Chapter 6</option> </select> </form>
</body> </BODY> </HTML>
</source>