Comment by PaulHoule

The thing most people never got about XSLT is that it is really about production rules -- and production rules (e.g. the major path to "expert systems") are one of the most solidly rejected technologies in software engineering.

I didn't understand this until I spent a few years going down a rabbit hole asking questions like "why don't people like production rules?" In the case of templating people expect to make a template with a top-down organization that looks like the output, whereas XSLT really wants you build transformations from the bottom-up. On some level the bottom-up part is clear, particularly if you want to code-generate your rules (towards the end I was writing production rules that write production rules) but what is not clear is how the parts all fit together: you can't visually tell between an XSLT that builds the structure you want vs one that doesn't.

I think the most fun I ever had with XSLT was when I used an XSLT engine with user-defined procedures and had them create side effects, such as matching certain patterns in an XML document and making SQL inserts, though that was a long time ago when we were still using terrible XML parsing libraries.