def register(*models, **kwargs):
    """
    Registers the given model(s) classes and wrapped ModelAdmin class with
    admin site:

    @register(Author)
    class AuthorAdmin(admin.ModelAdmin):
        pass

    A kwarg of `site` can be passed as the admin site, otherwise the default
    admin site will be used.
    """
    from .options import DocumentAdmin
    from .sites import AdminSite, site

    def _model_admin_wrapper(admin_class):
        admin_site = kwargs.pop('site', site)

        if not isinstance(admin_site, AdminSite):
            raise ValueError('site must subclass AdminSite')

        if not issubclass(admin_class, DocumentAdmin):
            raise ValueError('Wrapped class must subclass ModelAdmin.')

        admin_site.register(models, admin_class=admin_class)

        return admin_class

    return _model_admin_wrapper
