def get_urls(self):
        """
        Add ``layout_placeholder_data`` URL.
        """
        # See: `fluent_pages.pagetypes.fluentpage.admin.FluentPageAdmin`.
        urls = super(LayoutAdmin, self).get_urls()
        my_urls = patterns(
            '',
            url(
                r'^placeholder_data/(?P<id>\d+)/$',
                self.admin_site.admin_view(self.placeholder_data_view),
                name='layout_placeholder_data',
            )
        )
        return my_urls + urls