Someone from discourse.juliacn.com (the Chinese one) found this, I just translate for him. I think this is a bug? not what I expected.
julia> 1 .+ (1, 2)
(2, 3)
julia> 1 .+ 1 .+ (1, 2)
ERROR: MethodError: no method matching argtail()
Closest candidates are:
argtail(::Any, ::Any...) at essentials.jl:172
Stacktrace:
[1] tail(::Tuple{}) at ./essentials.jl:173
[2] longest_tuple(::Nothing, ::Tuple{}) at ./broadcast.jl:928 (repeats 3 times)
[3] longest_tuple(::Nothing, ::Tuple{Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{0},Nothing,typeof(+),Tuple{Int64,Int64}},Tuple{Int64,Int64}}) at ./broadcast.jl:927
[4] copy at ./broadcast.jl:920 [inlined]
[5] materialize(::Base.Broadcast.Broadcasted{Base.Broadcast.Style{Tuple},Nothing,typeof(+),Tuple{Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{0},Nothing,typeof(+),Tuple{Int64,Int64}},Tuple{Int64,Int64}}}) at ./broadcast.jl:724
[6] top-level scope at none:0