Clarify that (scheme r5rs) does not bind any identifiers that aren't present in the underlying implementation. So if the implementation does not have (scheme complex), then the corresponding identifiers (make-complex, magnitude, etc.) are not bound in (scheme r5rs).
What it now says:
Note that transcript-on and transcript-off are not present, and that exact and inexact appear under their R5RS names of inexact->exact and exact->inexact respectively. In addition, if an implementation does not provide a particular library such as the complex library, the corresponding identifiers will not appear in this library either.