6.2.X EE, 7.0.X, Master
The sitemaps generated by Liferay use the namespace "http://www.sitemaps.org/schemas/sitemap/0.9". The associated xsd file can be obtained at https://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd.
This xsd imposes an sequence order for the tags
Third-party services that validate the sitemap.xml against this xsd will issue an error if any of those tags are in the wrong order.
To see this error use the attached script in the Groovy console, using a valid url for the generated sitemap.xml (by going to localhost:8080/sitemap.xml and choosing the sitemap of a site).
Expected: The generated xml is valid against the xsd.