button_text is a standard character string (can be replaced by @) for the
text attached to the radio button. To change the text dynamically use %lc - Handle of Last Control and
the API function SetWindowText.
ctrl is 1 (on) or 0 (off).
grey_ctrl is 1 (enabled) or 0 (disable/greyed). A call-back function (if
present) is placed after this control variable.
%rb can be used in conjunction with the gang format code %ga - Gang Controls. Note that it is
not conventional to gang check boxes.