Address a few device related issues

spec/API_specification/array_object.md

@@ -1213,9 +1213,9 @@ Element-wise results must equal the results returned by the equivalent element-w
 ```
 
 (method-to_device)=
-### to\_device(self, device, /)
+### to\_device(self, device, /, *, stream=None)
 
-Move the array to the given device.
+Copy the array from the device it currently resides to the specified `device`.
 
 #### Parameters
 
@@ -1225,10 +1225,19 @@ Move the array to the given device.
 
 -   **device**: _<device>_
 
-    -   a `device` object (see {ref}`device-support`).
+    -   a `device` object (see {ref}`device-support`)
+
+-   **stream**: _Optional\[ Union\[ int, Any ]]_
+
+    -   stream object to use during copy. In addition to the supported types as discussed in {ref}`method-__dlpack__`, any library-specific stream object is also allowed to be used here.
 
 #### Returns
 
 -   **out**: _<array>_
 
-    -   an array with the same data and dtype, located on the specified device.
+    -   an array with the same data and dtype, located on the specified `device`.
+
+```{note}
+
+If `stream` is given, the copy operation will be enqueued on it; otherwise, it is enqueued on the default stream/queue (the concept of which is out of scope of this standard). Whether the copy is performed synchronously or asynchronously is up to the array library. As a result, if any synchronization (which is also out of scope of this standard) is required to guarantee data safety, the library should explain to its users.
+```

spec/design_topics/device_support.md

@@ -48,13 +48,20 @@ cross-device data transfer:
   libraries is out of scope).
 2. A `device=None` keyword for array creation functions, which takes an
    instance of a `Device` object.
-3. A `.to_device(device)` method on the array object, with `device` again being
-   a `Device` object, to move an array to a different device.
+3. A `.to_device` method on the array object, with `device` again being
+   a `Device` object, to copy an array to a different device.
 
 ```{note}
-The only way to obtain a `Device` object is from the `.device` property on
-the array object, hence there is no `Device` object in the array API itself
-that can be instantiated to point to a specific physical or logical device.
+In the current API standard, the only way to obtain a `Device` object is from the
+`.device` property on the array object, hence there is no `Device` object in the
+array API itself that can be instantiated to point to a specific physical or
+logical device. In other words, the standard does *not* include a universal
+`Device` object recognized by all compliant libraries.
+
+For array libraries that concern with multi-device support, including CPU and GPU,
+it is free to expose a library-specific device object for use (ex: creating an
+array on a particular device). For the purpose of this standard, it is considered
+an (important) implementation detail.
 ```