Register the supplied dictionary of associations between
        elements and plotting classes to the specified backend.

def register(cls, associations, backend, style_aliases={}):
        """
        Register the supplied dictionary of associations between
        elements and plotting classes to the specified backend.
        """
        if backend not in cls.registry:
            cls.registry[backend] = {}
        cls.registry[backend].update(associations)

        groups = Options._option_groups
        if backend not in cls._options:
            cls._options[backend] = OptionTree([], groups=groups)
        if backend not in cls._custom_options:
            cls._custom_options[backend] = {}

        for view_class, plot in cls.registry[backend].items():
            expanded_opts = [opt for key in plot.style_opts
                             for opt in style_aliases.get(key, [])]
            style_opts = sorted(set(opt for opt in (expanded_opts + plot.style_opts)
                                    if opt not in plot._disabled_opts))
            plot_opts = [k for k in plot.params().keys() if k not in ['name']]

            with param.logging_level('CRITICAL'):
                plot.style_opts = style_opts

            plot_opts =  Keywords(plot_opts,  target=view_class.__name__)
            style_opts = Keywords(style_opts, target=view_class.__name__)

            opt_groups = {'plot':   Options(allowed_keywords=plot_opts),
                          'output': Options(allowed_keywords=Options._output_allowed_kws),
                          'style': Options(allowed_keywords=style_opts),
                          'norm':  Options(framewise=False, axiswise=False,
                                           allowed_keywords=['framewise',
                                                             'axiswise'])}

            name = view_class.__name__
            cls._options[backend][name] = opt_groups