The following group of checkboxes requires at least one selection.
The following group of checkboxes allows at most one selection. This is different from a set of radio buttons, because radio buttons do not allow no selection.
The following group of checkboxes allows any number of selections. The state of the group can be changed by clicking the select-all box. The select-all box's state can also be changed by selecting all or un-checking one fewer than all.
If any of the following checkboxes are checked, then the buttons will be enabled.