[plt-scheme] Doc for "standard peek-char"

In the MzScheme manual, in Ch11, peek-char is described thus:

(peek-char [input-port skip-k]) extends the standard peek-char with an
optional argument (defaulting to 0) that represents the number of
bytes (not characters) to skip.

OK, um, where is the *standard* peek-char described?

I'm trying to find out what peek-byte (which is defined by reference
to peek-char) returns at eof.  Actually, that's easy to determine
empirically, but what DrScheme prints, "#<eof>" is not something I can
test for -- it's a syntax error to write

(= "#<eof>" (peek-byte port))

I understand that I most likely need to use something other than "="
as well, because I care about equivalence rather than identity.  Clue
on that would also be welcome (save me some silly hacking around).