Nothing to add, just here for reference.
“Everything is an X” is a very high level pattern that you see applied in the design of lots of systems, including programming languages and user interfaces. It has a lot of advantages, and some disadvantages. I’ll discuss some of these, then look at some examples, which will be necessary to understand what I’m really talking about.
When we say “everything” here, we’re talking very loosely — many things in the system are not, in fact, instances of “X”, but are something lower level, or just completely different. “Everything is an X” really means “a surprising number of things in this system are an X”.