I just leaned about EXI as it's being used on a project I work on. It's quite amazingly fast and small! It is a binary representation of the xml stream. It can compress quite small if you have an xmlschema to go with your xml.

I was curious about how it is implemented and I found the spec easy to read and quite elegant: https://www.w3.org/TR/exi/

That data transform thing xslt could do was so cool. You could twist it into emitting just about any other format and XML was the top layer. You want it in tab delimited yaml. Feed it the right style sheet and there you go. Other system wants CSV. Sure thing different style sheet and there you go.

For a transport tech XML was OK. Just wasted 20% of your bandwidth on being a text encoding. Plus wrapping your head around those style sheets was a mind twister. Not surprised people despise it. As it has the ability to be wickedly complex for no real reason.

84 years? nope.