The Reference Manual topic on the drop=true attribute, rrefattribdrop.dita, contains the statement,
"This attribute, like shutdown=true, cannot be combined with other attributes."
This used to be true, but with the addition of the deregister attribute, which must be combined with shutdown=true, it is now incorrect.
The sentence should be changed to say only,
"This attribute cannot be combined with other attributes."
(I'm assuming that the deregister attribute doesn't apply to dropping an in-memory database, since it's specific to the embedded driver. Please let me know if this isn't the case.)