What's going on at line 5 [db _] , something is being ignored '_'(does it have to). what is being ignored? | what's going on at line 11- what's path for?is it related to clojure.zip/path

example.cljs

(register-handler                 ;; setup initial state
  :initialize                     ;; usage:  (dispatch [:initialize])
  (fn
    [db _]
    (merge db initial-state)))    ;; what it returns becomes the new state


(register-handler
  :time-color                     ;; usage:  (dispatch [:time-color 34562])
  (path [:time-color])            ;; this is middleware
  (fn
    [time-color [_ value]]        ;; path middleware adjusts the first parameter
    value))


(register-handler
  :timer
  (fn
    ;; the first item in the second argument is :timer the second is the
    ;; new value
    [db [_ value]]
    (assoc db :timer value)))    ;; return the new version of db