SR> So if we were to start requiring 1.6 I would like to prepare by SR> adding a specific error message to mkgmap stating the version SR> requirements, rather than just a stack trace that you would SR> currently see, and to get a description of how to obtain 1.6 for the SR> different Macs that can be placed on the wiki and web site etc. I guess the problem is if you just compile with 1.6 and run on 1.5, the VM fails pretty quickly with a UnsupportedClassVersionError. Perhaps if you set <property name="ant.build.javac.target" value="1.5"/> and checking immediately on startup to see if eg NavigableSet exists you'll be able to do what you want? Might also have to avoid 1.6 language features like @Override on interface implementations I suppose. I'm quite happy to see a move to 1.6, but as you say being able to give a clear warning when running on 1.5 is probably essential to reduce the amount of support required. Chris