return ! empty( $to_set );

	}

	/**
	 * Get the Lesson's schema, conforming to JSON Schema.
	 *
	 * @since 1.0.0-beta.27
	 *
	 * @return array Item schema data.
	 */
	protected function get_item_schema_base() {

		$schema = (array) parent::get_item_schema_base();

		$lesson_properties = array(
			'parent_id'    => array(
				'description' => __( 'WordPress post ID of the parent item. Must be a Section ID. 0 indicates an "orphaned" lesson which can be edited and viewed by instructors and admins but cannot be read by students.', 'lifterlms' ),
				'type'        => 'integer',
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
			),
			'course_id'    => array(
				'description' => __( 'WordPress post ID of the lesson\'s parent course.', 'lifterlms' ),
				'type'        => 'integer',
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
				'readonly'    => true,
			),
			'order'        => array(
				'description' => __( 'Order of the lesson within its immediate parent.', 'lifterlms' ),
				'type'        => 'integer',
				'default'     => 1,
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
				'required'    => true,
			),
			'prerequisite' => array(
				'description' => __( 'Lesson ID of the prerequisite lesson.', 'lifterlms' ),
				'type'        => 'integer',
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
			),
			'points'       => array(
				'description' => __( 'Determines the weight of the lesson when grading the course.', 'lifterlms' ),
				'type'        => 'integer',
				'default'     => 1,
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
			),
			'audio_embed'  => array(
				'description' => __( 'URL to an oEmbed enable audio URL.', 'lifterlms' ),
				'type'        => 'string',
				'context'     => array( 'view', 'edit' ),
				'format'      => 'uri',
				'arg_options' => array(
					'sanitize_callback' => 'esc_url_raw',
				),
			),
			'video_embed'  => array(
				'description' => __( 'URL to an oEmbed enable video URL.', 'lifterlms' ),
				'type'        => 'string',
				'context'     => array( 'view', 'edit' ),
				'format'      => 'uri',
				'arg_options' => array(
					'sanitize_callback' => 'esc_url_raw',
				),
			),
			'drip_date'    => array(
				'description' => __(
					'The date and time when the lesson becomes available. Applicable only when drip_method is date. Format: Y-m-d H:i:s.',
					'lifterlms'
				),
				'type'        => 'string',
				'context'     => array( 'view', 'edit' ),
			),
			'drip_days'    => array(
				'description' => __( 'Number of days to wait before allowing access to the lesson. Applicable only when drip_method is enrollment, start, or prerequisite.', 'lifterlms' ),
				'type'        => 'integer',
				'default'     => 1,
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => 'absint',
				),
			),
			'drip_method'  => array(
				'description' => __(
					'Determine the method with which to make the lesson content available.
					<ul>
						<li>none: Drip is disabled; the lesson is immediately available.</li>
						<li>date: Lesson is made available at a specific date and time.</li>
						<li>enrollment: Lesson is made available a specific number of days after enrollment into the course.</li>
						<li>start: Lesson is made available a specific number of days after the course\'s start date. Only available on courses with a access_opens_date.</li>
						<li>prerequisite: Lesson is made available a specific number of days after the prerequisite lesson is completed.</li>
					</ul>',
					'lifterlms'
				),
				'type'        => 'string',
				'default'     => 'none',
				'enum'        => array( 'none', 'date', 'enrollment', 'start', 'prerequisite' ),
				'context'     => array( 'view', 'edit' ),
			),
			'public'       => array(
				'description' => __( 'Denotes a lesson that\'s publicly accessible regardless of course enrollment.', 'lifterlms' ),
				'type'        => 'boolean',
				'default'     => false,
				'context'     => array( 'view', 'edit' ),
			),
			'quiz'         => array(
				'description' => __( 'Associate a quiz with this lesson.', 'lifterlms' ),
				'type'        => 'object',
				'context'     => array( 'view', 'edit' ),
				'arg_options' => array(
					'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database().
					'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database().
				),
				'properties'  => array(
					'enabled'     => array(
						'description' => __( 'Determines if a quiz is enabled for the lesson.', 'lifterlms' ),
						'type'        => 'boolean',
						'default'     => false,
						'context'     => array( 'view', 'edit' ),
					),
					'id'          => array(
						'description' => __( 'The post ID of the associated quiz.', 'lifterlms' ),
						'type'        => 'integer',
						'default'     => 0,
						'context'     => array( 'view', 'edit' ),
						'arg_options' => array(
							'sanitize_callback' => 'absint',
						),
					),
					'progression' => array(
						'description' => __(
							'Determines lesson progression requirements related to the quiz.
							<ul>
								<li>complete: The quiz must be completed (with any grade) to progress the lesson.</li>
								<li>pass: A passing grade must be earned to progress the lesson.</li>
							</ul>',
							'lifterlms'
						),
						'type'        => 'string',
						'default'     => 'complete',
						'enum'        => array( 'complete', 'pass' ),
						'context'     => array( 'view', 'edit' ),
					),
				),
			),
		);