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 _theme_widget_style(layout, widget_style):

        row = layout.row()

        subsplit = row.split(percentage=0.95)

        padding = subsplit.split(percentage=0.15)
        colsub = padding.column()
        colsub = padding.column()
        colsub.row().prop(widget_style, "outline")
        colsub.row().prop(widget_style, "item", slider=True)
        colsub.row().prop(widget_style, "inner", slider=True)
        colsub.row().prop(widget_style, "inner_sel", slider=True)

        subsplit = row.split(percentage=0.85)

        padding = subsplit.split(percentage=0.15)
        colsub = padding.column()
        colsub = padding.column()
        colsub.row().prop(widget_style, "text")
        colsub.row().prop(widget_style, "text_sel")
        colsub.prop(widget_style, "show_shaded")
        subsub = colsub.column(align=True)
        subsub.active = widget_style.show_shaded
        subsub.prop(widget_style, "shadetop")
        subsub.prop(widget_style, "shadedown")

        layout.separator()