Checkmark class creates an image button with a checkmark that can have two different states. It is often used to toggle options. This class really just creates the checkmark button. It does not put a label next to it. If you want to have a label for your checkmark, you need to do this manually by placing a text or label object next to the checkmark.
Here is an example of how to create a checkmark with an adjacent label:
<hgroup> <label>Enable cool option</label> <checkmark/> </hgroup>