[boost] [proto] docs unclear (to me) for: "Expression Nodes as Fusion Sequences"

Hi! In the section "Expression Nodes as Fusion Sequences" you show the follwing code struct fun_t {}; terminal<fun_t>::type const fun = {{}}; // ... fusion::for_each( fusion::transform( // pop_front() removes the "fun" child fusion::pop_front(fun(1,2,3,4)) // Extract the ints from the terminal nodes , functional::arg<>() ) , display() ); It did not became clear to me why a terminal<fun_t>::type can be initialized with 4 integer arguments. I thought terminal<fun_t>::type is equivalent to expr< tag::terminal, args0< fun_t >, 0 > and should take no args at all. Could you clarify this? Markus