I am getting fairly good with XML, to the point I can do MOST of what I want ( with tons of assistance from the gurus in this room) but I must admit I accomplish too many things with trial and error as opposed to figuring it out beforehand. I have read Arne's treatise on XML as well as Nick Pikes, but there are still things that elude me, and if anyone could give simple explanations with examples I would really appreciate it.First off I am a non programmer teaching myself, so those of you well versed in programming logic have to forgive my ignorance.Can anyone explain in laymans term the way XML (RPN) uses the stacks? Q: (L:addrudder,percent) (L:AddruddControl,percent) != What does the "!" do?I think that "d" duplicates the last stack entry, but if thats the case, how does one determine which is the last stack entry?And I have NO idea what "?" does.ANY help is appreciatedSteve

!= simply means "not equal"

? is a 'shorthand' if statement.A B C 1 == ?If C = 1, put A on the stack, else put B on the stack.Then you can do whatever you want with the top of the stack:A B C 1 == ? (>L:AorB, unit)--Jon