PGconn structure - Mailing list pgsql-interfaces

Hello Friends,

I would like to know the structure of PGconn object of the libpq. I
have searched for this in libpq-fe.h  header file. unfortunately there
they write "The contents of this struct are not supposed to be known to
applications".
where can I found the information related to the structure of the
PGconn structure.

Thanks in Advance