[EXI] processing instruction

Hi EXI experts
    Should the first line of an XML file treated as a processing instruction
or is there any deviation for this. 
 
<?xml version="1.0" encoding="UTF-8"?>
........
........
 
Can it be under the control of the preserve.pi fidelity option. Otherwise
there is no way to convey the first line information in the EXI binary to
the decoder. If it is not as per preserve.pi then there can be chances of
improper decoding of some information completely.
 
The encoder can encode from xml with first line as 
    <?xml version="1.0"?>
and decoder can produce an xml with first line as
    <?xml version="1.0" encoding="UTF-8"?>
 
Also assuming that the encoder has encoded an XML file in some encoding
format 'x'. Then as per the above statement only when the pi is preserved
decoder will be able to decode the binary completely considering the same
encoding format 'x'.
 
regards
Santhanakrishnan