Automattic / jetpack

			// If it's an associative array, use the keys to check that the value is among those admitted.

			$enum = ( count( array_filter( array_keys( $args['enum'] ), 'is_string' ) ) > 0 ) ? array_keys( $args['enum'] ) : $args['enum'];

			if ( ! in_array( $value, $enum ) ) {

				return new WP_Error( 'invalid_param_value', sprintf(

					/* Translators: first variable is the parameter passed to endpoint that holds the list item, the second is a list of admitted values. */

					esc_html__( '%1$s must be one of %2$s', 'jetpack' ), $param, implode( ', ', $enum )

				) );

			}

		$modules = Jetpack::get_available_modules();

		if ( count( array_intersect( $value, $modules ) ) != count( $value ) ) {

			return new WP_Error( 'invalid_param_value', sprintf( esc_html__( '%s must be a list of valid modules', 'jetpack' ), $param ) );

		}

		return true;

	}

		$sharer = new Sharing_Service();

		$services = array_keys( $sharer->get_all_services() );

		if ( ! empty( $value ) && ! in_array( $value, $services ) ) {

			return new WP_Error( 'invalid_param', sprintf( esc_html__( '%s is not a registered custom sharing service.', 'jetpack' ), $param ) );

		}

		return true;

	}