ref_choice referential class allows to choose within several values with radiobuttons
listechoiceA character vector giving possible choices
labelA character, title of the box giving the possible choices
selectedAn Integer the initial selected value (as an index), first=1 used in gradio
Objects can be created by calls of the form
new("ref_choice", listechoice=character() ,label=character()
,selected=integer()).
Other referential objects: charge,ref_choice-method,
ref_checkbox-class,
ref_coe-class, ref_dc-class,
ref_df-class,
ref_horodate-class,
ref_list-class,
ref_par-class,
ref_parqual-class,
ref_parquan-class,
ref_period-class,
ref_stage-class,
ref_taxa-class,
ref_year-class