Don't shortcut macro expansion of non-parameter macros. It won't work once we have more kinds of expansion items than strings and arguments, viz., magic tokens for __FILE__ and __LINE__ and so on. (separate version of this applied against Joerg's changes, because we need to revert some of them)

#define BC //**/*
#define EC */**//

BC
comment?
EC

BC comment? EC

#define FOO(x) x
FOO(abc BC def EC ghi)

#define BAR(x, y) x y
BAR(abc BC def, ghi EC jkl)

BC
#define BAZ baz
EC
BAZ