I made a website based on XML documents and XSLT transformations about 20 years ago. I really liked the concept. The infrastructure could have been made much simpler but I guess I wanted to have an excuse to play with these technologies.
After spending months working on my development machine, I deployed the website to my VPS, to realize to my utter dismay that the XSLT module was not activated on the PHP configuration. I had to ask the (small) company to update their PHP installation just for me, which they promptly did.