about gauges.dtd for creating xml gauge

Hi,I'm a bit confusing about gauges.dtd. I suppose you should write xml gauge according to gauges.dtd, however, even the official aircraft gauges can't be validated by gauges.dtd. I don't know if it can't be validated, how can it works. And when I want to write gauge myself, if I create it according to gauges.dtd, will it works?Here's some example, spirit_levers.xml in Spirit_of_StLouis writes But in gauges.dtd, it defines only the followingATTLIST Click Kind CDATA 'LeftSingle' Repeat (Yes | No) 'No' MouseWheelFlip (Yes | No) 'No' Event CDATA #IMPLIED I think it's not supposed to write things like MouseWheelUp or MouseWheelDown. So, what I want to know if in what way I should write the xml file.By the way, I use XMLSpy to validate it. Thanks.Qi