event-seq documentation list some options mapped to their Java XMLInputFactory peer.
Given no more information, as a reader I would consult the Java documentation and assume the default values there described.
But the function event-seq actually sets it's own default values for the options coalescing and supporting-external-entities (true and false respectively), where the Java defaults are different (false and undefined respectively).
I suggest to document the default values in the Clojure code for the function event-seq and it's dependants mentioning the options (e.g. parse and parse-str).