I am taken aback by a typing error I don't understand, which did not occur with 
3.08.4.

File "as_xcaml/xdbs/xdbs_lib/xdbs_sql_translator.ml", line 36, characters 17-30:
Constraints are not satisfied in this type.
Type
Xdbs_sql_extensions.xdbs_ext Pxp_document.node
should be an instance of
('a Pxp_document.node #Pxp_document.extension as 'a) Pxp_document.node
make[1]: *** [as_xcaml/xdbs/xdbs_lib/xdbs_sql_translator.cmo] Error 2

I am trying to decypher what's going on. It would help me a lot to know if and 
what changes have been made in 3.09.0 to the typing of class expressions.

Alex