Source

File: wp-admin/includes/export.php

function wxr_post_taxonomy() {
		$post = get_post();

		$taxonomies = get_object_taxonomies( $post->post_type );
		if ( empty( $taxonomies ) ) {
			return;
		}
		$terms = wp_get_object_terms( $post->ID, $taxonomies );

		foreach ( (array) $terms as $term ) {
			echo "\t\t<category domain=\"{$term->taxonomy}\" nicename=\"{$term->slug}\">" . wxr_cdata( $term->name ) . "</category>\n";
		}
	}