Examples.  Also accept uppercase idents (and some keywords) as ids for attributes/extension nodes.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13373 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Doc.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13374 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Typo.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/extension_points@13375 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02