Go中的“ | =”运算符是什么意思？

I've found this operator |= and I'm wondering what it means

func getPageInfoMode(r *http.Request) (mode PageInfoMode) {
    for _, k := range strings.Split(r.FormValue("m"), ",") {
        if m, found := modeNames[strings.TrimSpace(k)]; found {
            mode |= m
        }
    }
    return
}

Is an inplace bitwise OR operator https://golang.org/ref/spec#Operators.

There are many others:

+    &     +=    &=     &&    ==    !=        
-    |     -=    |=     ||    <     <=        
*    ^     *=    ^=     <-    >     >=        
/    <<    /=    <<=    ++    =     :=        
%    >>    %=    >>=    --    !            
&^   &^=