Rationale:

It's clear what we wanted to say, we just failed to say it. This fixes it.

Proposed resolution:

Rewrite these conditions as:

(which & (ios_base::in|ios_base::out)) == ios_base::in

(which & (ios_base::in|ios_base::out)) == ios_base::out

(which & (ios_base::in|ios_base::out)) == (ios_base::in|ios_base::out) and way == either ios_base::beg or ios_base::end

Otherwise

In Section [stringbuf.virtuals], Table 90, the implication is that the four conditions should be mutually exclusive, but they are not. The first two cases, as written, are subcases of the third.

As written, it is unclear what should be the result if cases 1 and 2 are both true, but case 3 is false.