I'd like to learn enough to understand the statement "JSX is just a JS primary," and I can't find out what a "$lang primary" is in PLT. Can you point out some resources for me to figure this out?
The full name is primary expression. The meat of it is that a primary is usually just a literal value, identifier, or something in parentheses, but it varies based on the particular language.
For a deep dive you'll want to read resources about parsing. To name one article that came up recently on HN, take a look at "Why Parsing Tools are Hard" [0].
