Do not assume all pages have changed

`<lastmod>` [is an optional tag](http://www.sitemaps.org/protocol.html#lastmoddef).

Including it as we currently do has the advantage of letting search engines know if nothing on the site has changed for quite a while (as in, the site has not been regenerated), but the disadvantage of telling search engines that every page on the site has changed each time the site is regenerated, even if no pages have been updated.

I'm not really sure which is worse&hellip;