Multiple Options Selected using checkbox

Im currently using the following code:

<perch:content order="4" id="category" type="radio" multiple="true" label="Choose Category" options="Injury Advice|injuryadvice, Stretching Exercises|stretching, Foam Roller|foamroller, Basic Pelvic Stability|pelvic, Back Rehab|backrehab, Neck Rehab|neckrehab, Shoulder Rehab|shoulderrehab, Hip Rehab|hiprehab, Thigh Rehab|thighrehab, Knee Rehab|kneerehab, Lower Leg Rehab|lowerle" />

But the client needs to be able to select multiple options so I thought I'd use a checkbox but it doesn't say in the documentation about multiple options using a checkbox .. any suggestions?