.. (two dots) as a operator name

General Usage
4

Yes. It’s not .. that’s special, but ..., since it is handled specially during lowering:

julia> Meta.@lower add(xs...) = reduce(+, xs)
:($(Expr(:thunk, CodeInfo(
    @ none within `top-level scope`
1 ─      $(Expr(:thunk, CodeInfo(
    @ none within `top-level scope`
1 ─     return $(Expr(:method, :add))
)))
│        $(Expr(:method, :add))
│   %3 = Core.Typeof(add)
│   %4 = Core.apply_type(Vararg, Core.Any)
│   %5 = Core.svec(%3, %4)
│   %6 = Core.svec()
│   %7 = Core.svec(%5, %6, $(QuoteNode(:(#= REPL[2]:1 =#))))
│        $(Expr(:method, :add, :(%7), CodeInfo(
    @ REPL[2]:1 within `none`
1 ─ %1 = reduce(+, xs)
└──      return %1
)))
└──      return add
))))

You can’t override the splatting/slurping operator.