extrapolation syntax?

[dlfivefifty]

It's sometimes helpful to use an OP on a domain bigger than the support of its weight. What syntax to use?

We are already using Base.unsafe_getindex for extrapolation at a point, so we could support, e.g.,

T_ext = Base.unsafe_getindex(Chebyshev(), Inclusion(-2..2), :)

though perhaps that's not explicit enough.

There's also the question of what type T_ext should be. SuperQuasiArray (as opposed to SubQuasiArray)?