wxr_site_url()

Source

File: wp-admin/includes/export.php

function wxr_site_url() {
		if ( is_multisite() ) {
			// Multisite: the base URL.
			return network_home_url();
		} else {
			// WordPress (single site): the blog URL.
			return get_bloginfo_rss( 'url' );
		}
	}