C++23 introduced `mdspan` ([[P0009R18]](https://wg21.link/p0009r18)), a non-owning multidimensional array abstraction that has a customizable layout. Layout customization was originally motivated in [[P0009R18]](https://wg21.link/p0009r18) with considerations for interoperability and performance, particularly on different architectures. Moreover, [[P2630R4]](https://wg21.link/p2630r4) introduced `submdspan`, a slicing function that can yield arbitrarily strided layouts. However, without standard library support, copying efficiently between `mdspan`s with mixes of complex layouts is challenging for users.