Meaning of ! and ? in Stockfish output? I've just installed Stockfish 8 and in the engine output, I see it has started to put ! and ? in various places (after certain moves and scores).  Example output:

    mover viewpoint     fewer / Multi-PV setting = 1 / more
exclude: none best +tail                                          
dep score   nodes   time    (not shown:  tbhits knps    seldep)
 24 +7.48   19.8M   0:12.09 Rd8+ Nd2 Nd5 Ne2 Nd7 Bd4 Rac8 Nc3 Nxc3+ Bxc3 Rc7 Ke2 Nb6 Rad1 Nd5 Be5 Rcc8 Ne4 f6 Bh3 Rc6 Bd4 b6 c3 h6 Kf2 Kf7 Rhe1 Ne7 Kf3 Nf5
 23 +7.42   14.4M   0:08.71 Rd8+ Nd2 Nd5 Ne2 b6 Bf2 Nc6 c3 Nce7 Nd4 b5 a3 Rab8 Kc2 a6 Rad1 Rbc8 Rhe1 h6 N2f3 Rd6 Kb1 g6 Kc2 Kg7 Nd2 Rd7 Ne4 Rdd8 Nf3 Nf5
 23 +7.25?  11.2M   0:06.78 Rd8+ Nd2?
 23 +7.16!  10.9M   0:06.62 Rd8+!
 23 +7.27!  10.7M   0:06.51 Rd8+!
 23 +7.34?  9.48M   0:05.73 Rd8+ Nd2?
 22 +7.27   7.93M   0:04.76 Rd8+ Nd2 Nd5 Ne2 b6 Bf2 Nc6 c3 Nce7 Nd4 b5 a3 Rab8 Kc2 a6 Rad1 h5 N2f3 g6 Ne5 Rbc8 Rhe1 h4 Nef3 hxg3 hxg3
 22 +7.30?  6.70M   0:03.99 Rd8+ Nd2?
 22 +7.22?  5.96M   0:03.56 Rd8+ Nd2?
 21 +7.15   5.11M   0:03.04 Rd8+ Nd2 Nd5 Ne2 b6 Bf2 Nd7 c3 N7f6 Bf3 a6 Kc2 b5 a4 Rac8 axb5 axb5 Bd4 Ne8 Rhd1 Nd6 Ra7 Nf5
 20 +7.14   2.80M   0:01.65 Rd8+ Nd2 Nd5 Ne2 b6 Bf2 Nd7 c3 Rac8 Kc2 N7f6 Bf3 a6 a4 b5 axb5 axb5 Bd4 Rd7 Bxf6 Ne3+ Kc1 gxf6 Nd4 b4 Bc6 Rdc7 cxb4


It did not do this previously.  What do these mean?
OK I just realized that I upgraded Winboard at the same time and it's actually Winboard that is now adding the ! and ?.  The meaning seems to be given on this page:


  A question mark as the last character in the pv field should be used to indicate the reported score is from a fail low, and thus represents an upper bound only. Similarly, an exclamation point should be used to indicate a fail high / lower bound.