I meant that a slicing operation referencing a single value in one axis but multiple values in all others returns an array with 1 less dimension, e.g. `arr[..., 0].ndim == arr.ndim - 1`. Of course, then concatenation is not possible with the original...

This restores the missing singleton dimension to allow concatenation. It isn't the shape after slicing. After slicing, the result needs to be reshaped to `pad_singleton`.

That said, I do think it can be stated clearer, perhaps `# Restore singleton dimension after slicing edge for concatenation`.