What is a CheckBox Group?
Image to have same checkbox in a form and each one can be a category, and you need the user choose minimum one or more category. With this behavior you define a group of checkbox and validate toghether to be sure the user check what you need.
To create a group of checkbox you must insert in your form some standard checkbox and add to them the special attribute dwzGroup like:

<input name="chk_1" dwzGroup="CheckGroup" type="checkbox" id="chk_1" value="1" />
<input name="chk_2" dwzGroup="CheckGroup" type="checkbox" id="chk_2" value="2" />
<input name="chk_3" dwzGroup="CheckGroup" type="checkbox" id="chk_3" value="3" />

the valur of the dwzGroup special attribute is the Name of the Group and in the behavior fields panel you will find a single line for all this checkbox with the value of the dwzGroup attribute in the Field name column.