Why does DrRacket IDE considers some identifiers as "symbols" and some as "keywords"? What is the difference?

Question

Why does DrRacket (kind of Scheme) IDE highlights some of the identifiers as "keywords" (for example define, lambda, send*), and the others as "symbols" (user defined identifiers, +, -, abs, send, send+, etc.)?

I am particularly confused by the difference between send* and send+. For reference, here are the beginnings of their definitions:

(define-syntax (send* stx) ...

(define-syntax (send+ stx) ...

(It is possible that I do not use the terms "identifier", "symbol", and "keyword" completely correctly, but this is how some of them seem to be used in DrRacket preferences.)

Unless this is a bug, it must be explained by the language "semantics", so I decided to ask here.

Answer 1

DrRacket maintains a list of keywords that it understands for auto-indentation, which you can find in the Preferences (under Editing->Indenting). If an identifier is listed as a keyword for indentation, then DrRacket will also highlight it differently if the chosen color scheme differentiates keywords from plain identifiers.

Identifiers like + are not highlighted because they are just names of functions, not "special forms" like if and cond. On the other hand, send+ isn't highlighted just because the default DrRacket keywords don't contain every syntactic form provided by Racket.