@prefix : <content.n3#> .

:test1 :is """@prefix log:  <http://www.w3.org/2000/10/swap/log#>.

{<> log:content ?x} => {:test1 :is ?x} .

{_:bn log:content ?x} => {:test2 a :FAILURE} .

{1 log:content ?x} => {:test3 a :FAILURE} .

{"foo" log:content ?x} => {:test4 a :FAILURE} .
""" .