The way it works is simple. It reads .xml files and uses the data in those files to make web pages with standardized templating. The output by default are valid XHTML 5.0, and as such, your input needs to be valid XML/XHTML for it to work.
The Site.PHP alpha testing builds had its first Git commit uploaded on 2025-06-28. Currently there are no formal releases. At this time, there are no public builds available.