I've been generating XML using nokogiri and jruby. On occasion, to stdout is printed the following text: "DEAD: marking instr dead!!". I can actually see where that is being generated in the jruby source (line 85 of LocalOptimizationPass.java, to be precise), but I don't know enough about jruby internals to determine whether this is something to be concerned about, or whether the System.out.println line was left in accidentally. I do notice the otherSystem.out.println calls are commented out so perhaps that is the case? FWIW, I've seen the behaviour in both 9.0.4.0 and 9.0.5.0.