code: def add(class_, name, value, sep=';'):
  		
  		values = class_.get_values_list(name, sep)
  		if value in values:
  			return
  		new_value = sep.join(values + [value])
  		winreg.SetValueEx(
  			class_.key, name, 0, winreg.REG_EXPAND_SZ, new_value)
  		class_.notify()
docs: Add a value to a delimited variable, but only when the value isn't
  		already present.