QU connects quotation marks, delimiting quoted sentences.

        +------------QUc-----------+               
        +-----------Xc-----------+ |               
        +------>WV----->+        | |               
        +---Wd---+      |        | +----CP---+     
        +-QUd-+  +-Sp*i-+--QI-+  | +Wd+--Ss--+-Xp-+
        |     |  |      |     |  | |  |      |    |
    LEFT-WALL " I.p wonder.v how , " she said.q-d . 

                     +---------QUc---------+
                     +---------Xc--------+ |
                     +----Wi----+        | |
        +---->WV---->+--QUd-+   |        | |
        +--Wd--+--Ss-+-Xc-+ |   +--I--+  | |
        |      |     |    | |   |     |  | |
    LEFT-WALL he said.q-d , " let's go.v ! "