The builtin macro prelude is very similar to the language prelude in that it is still available even with no_implicit_prelude, but it differs in that:

1. it only contains function-style macros
2. it is not available to no_core crates

It contains macros like option_env and line. A full list is available in library/std/src/lib.rs.

I would like the reference to have a section on them so that rustdoc can provide a banner on builtin macros linking to the reference's section on builtin macros.