API: Specify that DLPack should use BufferError (#498)

* API: Specify that DLPack should use BufferError

I would actually like MUST, but since most implementations currently don't
actually give a ``BufferError``, writing it as SHOULD instead.

First part of closing numpy/numpy#20742

* Fix duplicated word

Co-authored-by: Sebastian Berg <[email protected]>
Co-authored-by: Athan <[email protected]>

Author: seberg

Diff for: spec/API_specification/array_api/array_object.py

@@ -290,6 +290,15 @@ def __dlpack__(self: array, /, *, stream: Optional[Union[int, Any]] = None) -> P
         -------
         capsule: PyCapsule
             a DLPack capsule for the array. See :ref:`data-interchange` for details.
+
+        Raises
+        ------
+        BufferError
+            Implementations should raise ``BufferError`` when the data cannot
+            be exported as DLPack (e.g., incompatible dtype or strides). Other
+            errors are raised when export fails for other reasons (e.g., incorrect
+            arguments passed or out of memory).
+
         """
 
     def __dlpack_device__(self: array, /) -> Tuple[Enum, int]: