The size is going to depend on the set of features enabled and I expect that build has everything turned on so that it can be used for all the demos.

I did a quick check of a CM6 project (customizing the JS lexer) with the base options and a JS-derived lexer and it came out to 405k / 124k gzip. I wouldn't consider it especially lightweight but I think the size is reasonable for the feature set.

Hmm, not sure.

Here it is around 300kb inflated https://codemirror-basic-setup.replitfaris.repl.co/ using the basic-setup package, and I don't think this build tree-shakes.

Code for this build is here https://codemirror-basic-setup.replitfaris.repl.co/__repl