Nice read. It could probably save me a lot of time when writing few complex macros.
I can't find if you mention that "/// comment" is just a syntax sugar for #[doc=" comment"]. This may probably be useful in "Enum parsing" section (originally I used to think that the comments are not language items).
Actually, if the "Building Blocks" chapter gets significantly larger, I'll be tempted to have a matching cargo crate so that they're all immediately usable
I'm thinking of some building block for parsing enums and structs. So that serialization libraries, visitors and other useful tools do not need syntax extensions. Think of macro version of "#[derive(..)]". But I'm not sure how this thing could look like in generic way.
Is there a big, complicated macro that you'd like to see explained
Probably quick-error is a good candidate