def prepender(func):
    """
    Prepends some text to the *second* argument with which function `func` has been called.
    The *first* argument is a reference (`self`) to an instance of class Terms or one of its sub classes.
    `self` is accessed to look for a prefix `_prefix` to append to the second argument.

    This function is meant to be used as decorator.
    """
    def prepend(self, *args):
        prepended = self._prefix + args[0]
        return func(self, prepended, *args[1:])
    return prepend