sub f0    { my ($cb) = @_; '...' }
sub f1(&) { my ($cb) = @_; '...' }

f0(\&abc);                  # OK No error
f0(\&{ maybe_coderef() });  # OK Error caught at run-time (if any)
f0("abc");                  # XX Error uncaught
f0(maybe_coderef());        # XX Error uncaught (if any)

f1(\&abc);                  # OK No error
f1(\&{ maybe_coderef() });  # OK Error caught at run-time (if any)
f1("abc");                  # OK Error caught at compile-time
f1(maybe_coderef());        # OK Error caught at compile-time (if any)