What might be useful would be for `BaseArrays`

to be defined as follows.

```
julia> const CoreArrays{T,N} = Union{subtypes(Core, AbstractArray{T,N})...}
Union{Core.Compiler.AbstractRange{T}, Core.Compiler.BitArray{N}, Core.Compiler.ExceptionStack, Core.Compiler.MethodList, DenseArray{T, N}, Core.Compiler.LinearIndices{N, R} where R<:Tuple{Vararg{Core.Compiler.AbstractUnitRange{Int64}, N}}} where {T, N}
julia> const BaseArrays{T,N} = Union{subtypes(Base, AbstractArray{T,N})...}
Union{AbstractRange{T}, BitArray{N}, Base.ExceptionStack, Base.MethodList, LinearIndices{N, R} where R<:Tuple{Vararg{AbstractUnitRange{Int64}, N}}, Base.LogicalIndex{T}, Base.ReinterpretArray{T, N, S} where S, Base.ReshapedArray{T, N}, Base.SCartesianIndices2, SubArray{T, N}, CartesianIndices{N, R} where R<:Tuple{Vararg{OrdinalRange{Int64, Int64}, N}}, PermutedDimsArray{T, N}} where {T, N}
julia> const BaseAndCoreArrays{T,N} = Union{CoreArrays{T,N}, BaseArrays{T,N}}
Union{AbstractRange{T}, BitArray{N}, Base.ExceptionStack, Base.MethodList, Core.Compiler.AbstractRange{T}, Core.Compiler.BitArray{N}, Core.Compiler.ExceptionStack, Core.Compiler.MethodList, DenseArray{T, N}, LinearIndices{N, R} where R<:Tuple{Vararg{AbstractUnitRange{Int64}, N}}, Base.LogicalIndex{T}, Base.ReinterpretArray{T, N, S} where S, Base.ReshapedArray{T, N}, Base.SCartesianIndices2, SubArray{T, N}, Core.Compiler.LinearIndices{N, R} where R<:Tuple{Vararg{Core.Compiler.AbstractUnitRange{Int64}, N}}, CartesianIndices{N, R} where R<:Tuple{Vararg{OrdinalRange{Int64, Int64}, N}}, PermutedDimsArray{T, N}} where {T, N}
julia> foo(x::BaseAndCoreArrays) = x[1]
foo (generic function with 1 method)
julia> foo([4,5,6])
4
julia> foo(x::BaseAndCoreArrays) = x[1:length(x)]
foo (generic function with 1 method)
julia> foo([4,5,6])
3-element Vector{Int64}:
4
5
6
```

Then you could happily define `foo(A::BaseAndCoreArrays)`

without worrying about â€śstrangeâ€ť arrays.

```
julia> foo(x::BaseAndCoreArrays) = x[1]
foo (generic function with 1 method)
julia> foo([4,5,6])
4
julia> foo(x::BaseAndCoreArrays) = x[1:length(x)]
foo (generic function with 1 method)
julia> foo([4,5,6])
3-element Vector{Int64}:
4
5
6
```