Addressing feedback

Author: przemektmalon

sycl/doc/extensions/experimental/sycl_ext_oneapi_memory_export.asciidoc

@@ -255,6 +255,9 @@ The value of `ExternalMemHandleType` must match the value passed to
 `ExternalMemHandleType` value that not match the value passed to
 `alloc_exportable_device_mem` results in undefined behavior.
 
+The implementation of this function does not have to be defined for every value
+of the `external_mem_handle_type` enum.
+
 The `syclDevice` and `syclContext` passed to `export_device_mem_handle` must
 match the device and context used when the `deviceMemory` was allocated using
 `alloc_exportable_device_mem`. If a `syclQueue` is passed, it must also be
@@ -354,6 +357,18 @@ We are considering this approach for future versions of this extension, but for
 this initial draft we've have decided to provide explicit APIs to simplify the
 implementation and gather early feedback.
 
+=== Querying Supported External Memory Handle Types
+
+Currently, there is no way to query which external memory handle types are
+supported by the implementation. As this is an initial draft of an
+experimental extension intended to gather early feedback, we have not
+implemented this functionality yet. However, we are aware of this limitation
+and plan to address it in future versions of this extension.
+
+As noted above in the document, the {dpcpp} implementation currently
+supports exporting memory with the `opaque_fd` and `win32_nt_handle` handle
+types, and only on the Level Zero backend.
+
 == Revision History
 
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