= variable: interrogate a button variable     variable var ?value? Variable  queries  or  sets  the  value  of a Tk radiobutton,checkbutton or choicebutton variable.   An  error  diagnosticwill be returned if the variable is of the wrong type (if forinstance it is the name of a named channel). If value is given, the value of the variable is set  to  thatvalue,  and  any associated buttons will subsequently reflectthis  in  their  appearance.   Omitting  the  value  argumentreturns the current value of the variable. The  special variable lasterror holds the text of the last Tkerror encountered.  It resets when queried. == see ALSOcheckbutton(9), choicebutton(9), radiobutton(9)