NEP-{13, 18} could and should use common codebase where possible. This issue is a follow up from #6632 (comment).

For example:

• chunk_types has both is_valid_chunk_type (NEP-18) and is_valid_array_chunk (NEP-13), this could be simplified and consolidated
• __array_function__ (NEP-18) should probably generalise _should_delegate and both __array_ufunc__ (NEP-13) and __array_function__ (NEP-18) should just use general _should_delegate

Environment:

• Dask version: 2.17.0/master