Fischer offers to exchange rooks which would leave him, and not Black, in control of the e file.
Note that the pawn hanging at d5 since move 9 is still hanging. By some White's 28th move is
regarded as inferior, as it breathes new life into Black's attack.
26. ... Rae8
27. Rae1 Be5
28. Qb4 Qh6
29. h4 g5