xs:nil feature in compression mode

Dear all,

This is feedback we have related to the EXI specification.

The wording of @xsi:nil in section 9.2.1 seems slightly out of sync.
The inclusion within or without the structure channel of the @xsi:nil value happens if @xsi:nil "has a schema-valid value".
I would reword it so that we phrase in terms of the @xsi:nil values being encoded using the  Boolean representation.
This does not change the behavior and I find it clearer this way.

Regards,
                Youenn