I'm not sure what you're asking. A checkbox has a label and a single value. Values may be different from labels. Please explain what you mean about comma separated data? How do you envision using them with a checkbox? Provide an example.

okay... i have a signup Form with a checkboxgroup with multiple entries and this is stored after submitting as a usermeta entrie... now i want to display this usermeta entrie as an checkboxgroup in an other form with selected entries based on the usermeta entrie or entries...