Try this:
inherits(instance, "envRefClass")
# should return [1] TRUE
This is found in the "Inheritance" section of help(ReferenceClasses)
. And I suspect that John Chambers might object to calling this "dirty".
Apropos Hadley's comment, is
is documented to behave mostly the same as inherits
but has the added capacity to recognize conditional inheritance:
is(instance, "envRefClass")
#TRUE