Source

File: wp-includes/sitemaps/class-wp-sitemaps.php

public function register_sitemaps() {
		$providers = array(
			'posts'      => new WP_Sitemaps_Posts(),
			'taxonomies' => new WP_Sitemaps_Taxonomies(),
			'users'      => new WP_Sitemaps_Users(),
		);

		/* @var WP_Sitemaps_Provider $provider */
		foreach ( $providers as $name => $provider ) {
			$this->registry->add_provider( $name, $provider );
		}
	}