Source

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

public function register_rewrites() {
		// Add rewrite tags.
		add_rewrite_tag( '%sitemap%', '([^?]+)' );
		add_rewrite_tag( '%sitemap-subtype%', '([^?]+)' );

		// Register index route.
		add_rewrite_rule( '^wp-sitemap\.xml$', 'index.php?sitemap=index', 'top' );

		// Register rewrites for the XSL stylesheet.
		add_rewrite_tag( '%sitemap-stylesheet%', '([^?]+)' );
		add_rewrite_rule( '^wp-sitemap\.xsl$', 'index.php?sitemap-stylesheet=sitemap', 'top' );
		add_rewrite_rule( '^wp-sitemap-index\.xsl$', 'index.php?sitemap-stylesheet=index', 'top' );

		// Register routes for providers.
		add_rewrite_rule(
			'^wp-sitemap-([a-z]+?)-([a-z\d_-]+?)-(\d+?)\.xml$',
			'index.php?sitemap=$matches[1]&sitemap-subtype=$matches[2]&paged=$matches[3]',
			'top'
		);
		add_rewrite_rule(
			'^wp-sitemap-([a-z]+?)-(\d+?)\.xml$',
			'index.php?sitemap=$matches[1]&paged=$matches[2]',
			'top'
		);
	}