Query parameter separator value

Reading the specification, it seems that the only constraint on the 
separator value is to be a xml string of length 1.
It would therefore be possible to have a separator value that needs to 
be %-encoded in the URL (e.g. queryParameterSeparator="é").
I do not know whether that was intended but in this case, the query 
string may become ambiguous: if the separator value appears in a 
parameter value, it will be %-encoded exactly like the separator value. 
It might be safer to restrict the separator value range.

In any case, the most sensible values are '&' and ';'. Is there any 
other obvious possibility?
While '&' is the default value, ';' does not appear AFAIKT neither in 
the spec nor in the primer.
It might therefore be good to add a statement that tells a word about 
these values, maybe as a SHOULD.
Regards,
    Youenn