WP_REST_Terms_Controller::get_collection_params

	public function get_collection_params() {
		$query_params = parent::get_collection_params();
		$taxonomy     = get_taxonomy( $this->taxonomy );

		$query_params['context']['default'] = 'view';

		$query_params['exclude'] = array(
			'description' => __( 'Ensure result set excludes specific IDs.' ),
			'type'        => 'array',
			'items'       => array(
				'type' => 'integer',
			),
			'default'     => array(),
		);

		$query_params['include'] = array(
			'description' => __( 'Limit result set to specific IDs.' ),
			'type'        => 'array',
			'items'       => array(
				'type' => 'integer',
			),
			'default'     => array(),
		);

		if ( ! $taxonomy->hierarchical ) {
			$query_params['offset'] = array(
				'description' => __( 'Offset the result set by a specific number of items.' ),
				'type'        => 'integer',
			);
		}

		$query_params['order'] = array(
			'description' => __( 'Order sort attribute ascending or descending.' ),
			'type'        => 'string',
			'default'     => 'asc',
			'enum'        => array(
				'asc',
				'desc',
			),
		);

		$query_params['orderby'] = array(
			'description' => __( 'Sort collection by term attribute.' ),
			'type'        => 'string',
			'default'     => 'name',
			'enum'        => array(
				'id',
				'include',
				'name',
				'slug',
				'include_slugs',
				'term_group',
				'description',
				'count',
			),
		);

		$query_params['hide_empty'] = array(
			'description' => __( 'Whether to hide terms not assigned to any posts.' ),
			'type'        => 'boolean',
			'default'     => false,
		);

		if ( $taxonomy->hierarchical ) {
			$query_params['parent'] = array(
				'description' => __( 'Limit result set to terms assigned to a specific parent.' ),
				'type'        => 'integer',
			);
		}

		$query_params['post'] = array(
			'description' => __( 'Limit result set to terms assigned to a specific post.' ),
			'type'        => 'integer',
			'default'     => null,
		);

		$query_params['slug'] = array(
			'description' => __( 'Limit result set to terms with one or more specific slugs.' ),
			'type'        => 'array',
			'items'       => array(
				'type' => 'string',
			),
		);

		/**
		 * Filter collection parameters for the terms controller.
		 *
		 * The dynamic part of the filter `$this->taxonomy` refers to the taxonomy
		 * slug for the controller.
		 *
		 * This filter registers the collection parameter, but does not map the
		 * collection parameter to an internal WP_Term_Query parameter.  Use the
		 * `rest_{$this->taxonomy}_query` filter to set WP_Term_Query parameters.
		 *
		 * @since 4.7.0
		 *
		 * @param array       $query_params JSON Schema-formatted collection parameters.
		 * @param WP_Taxonomy $taxonomy     Taxonomy object.
		 */
		return apply_filters( "rest_{$this->taxonomy}_collection_params", $query_params, $taxonomy );
	}