Parameters for importing an opaque fd from non-Vulkan sources

VUID-VkMemoryAllocateInfo-memoryTypeIndex-00648 states:
> If the parameters define an import operation and the external handle is a POSIX file descriptor created outside of the Vulkan API, the value of `memoryTypeIndex` **must** be one of those returned by [vkGetMemoryFdPropertiesKHR](https://www.khronos.org/registry/vulkan/specs/1.3-extensions/man/html/vkGetMemoryFdPropertiesKHR.html)

`vkGetMemoryFdProperties` forbids giving it a handle type of `VK_EXTERNAL_MEMORY_HANDLE_TYPE_OPAQUE_FD_BIT`. If this is used as the handle type, then VUID-VkMemoryAllocateInfo-allocationSize-01742 states what the `allocationSize` and `memoryTypeIndex` should be if the file descriptor comes from Vulkan. But if the user is importing memory with this handle type from a non-Vulkan source, there are no VUIDs restricting these values. Is anything allowed? Or is this handle type forbidden for non-Vulkan file descriptors?