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 draw(self, context):
        layout = self.layout

        layout.operator(
                "wm.url_open", text="Add-ons Catalog", icon='URL',
                ).url = "http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts"

        layout.separator()

        layout.operator(
                "wm.url_open", text="How to share your add-on", icon='URL',
                ).url = "http://wiki.blender.org/index.php/Dev:Py/Sharing"
        layout.operator(
                "wm.url_open", text="Add-on Guidelines", icon='URL',
                ).url = "http://wiki.blender.org/index.php/Dev:2.5/Py/Scripts/Guidelines/Addons"
        layout.operator(
                "wm.url_open", text="API Concepts", icon='URL',
                ).url = bpy.types.WM_OT_doc_view._prefix + "/info_quickstart.html"
        layout.operator("wm.url_open", text="Add-on Tutorial", icon='URL',
                ).url = "http://www.blender.org/api/blender_python_api_current/info_tutorial_addon.html"