WP_REST_Controller::get_endpoint_args_for_item_schema

			// Arguments specified as `readonly` are not allowed to be set.
			if ( ! empty( $params['readonly'] ) ) {
				continue;
			}

			$endpoint_args[ $field_id ] = array(
				'validate_callback' => 'rest_validate_request_arg',
				'sanitize_callback' => 'rest_sanitize_request_arg',
			);

			if ( isset( $params['description'] ) ) {
				$endpoint_args[ $field_id ]['description'] = $params['description'];
			}

			if ( WP_REST_Server::CREATABLE === $method && isset( $params['default'] ) ) {
				$endpoint_args[ $field_id ]['default'] = $params['default'];
			}

			if ( WP_REST_Server::CREATABLE === $method && ! empty( $params['required'] ) ) {
				$endpoint_args[ $field_id ]['required'] = true;
			}

			foreach ( $valid_schema_properties as $schema_prop ) {
				if ( isset( $params[ $schema_prop ] ) ) {
					$endpoint_args[ $field_id ][ $schema_prop ] = $params[ $schema_prop ];
				}
			}

			// Merge in any options provided by the schema property.
			if ( isset( $params['arg_options'] ) ) {

				// Only use required / default from arg_options on CREATABLE endpoints.
				if ( WP_REST_Server::CREATABLE !== $method ) {
					$params['arg_options'] = array_diff_key(
						$params['arg_options'],
						array(
							'required' => '',
							'default'  => '',
						)
					);
				}

				$endpoint_args[ $field_id ] = array_merge( $endpoint_args[ $field_id ], $params['arg_options'] );
			}
		}

		return $endpoint_args;
	}

	/**
	 * Sanitizes the slug value.
	 *
	 * @since 4.7.0
	 *
	 * @internal We can't use sanitize_title() directly, as the second