Inout table

[nkm1 via Digitalmars-d-learn]

There is this little table in 
https://dlang.org/spec/function.html#inout-functions:

Common qualifier of the two type qualifiers
                   mutable const  immutable inout inout const
mutable (= m)      m       c      c         c     c
const (= c)        c       c      c         c     c
immutable (= i)    c       c      i         wc    wc
inout (= w)        c       c      wc        w     wc
inout const (= wc) c       c      wc        wc    wc
I don't understand what it is trying to say. What is it that is 
calculated here? The qualifier for the return value?
And what's an "inout const"?