[whatwg] XMLHttpRequest for missing file

The XMLHttpRequest spec has this to say about failed loads:

<snip>
The NETWORK_ERR exception is thrown when a network error occurs in  
synchronous requests.
...
In case of network errors

In case of DNS errors or other type of networks run the following set  
of steps.This does not include HTTP responses that indicate some type  
of error, such as HTTP status code 410.
</snip>

What should happen with failed file:/// URL loads? For example, what  
if the file doesn't exist?

Thanks,
Geoff