def add(self, elem, replace=False):
        """Add a requirement.

        :param elem: a string or :class:`Requirement` instance.
        :param replace: if `True`, packages in the set with the same name will
            be removed first.
        """
        if isinstance(elem, text_type):
            elem = Requirement.coerce(elem)
        if replace and elem in self:
            self.remove(elem)
        super(Requirements, self).add(elem)
def __init__(self, parent, window):
		self._parent = parent
		self._window = window
		self._application = self._parent._application

		# create user interface
		self._container = gtk.VBox(False, 5)
		self._controls = gtk.HBox(False, 5)

		separator = gtk.HSeparator()

		# pack interface
		self._container.pack_end(separator, False, False, 0)
		self._container.pack_end(self._controls, False, False, 0)