Undoubtedly, you've heard of Extensible Markup Language, commonly known as XML. You may have even seen some of it, though you might not have been aware of it at the time. One thing's fairly certain, however: You'll be seeing a lot more of it in the future. My certainty is based on the fact that XML is beginning to spread at a pace that almost justifies the hype that accompanied its introduction, now that commercial vendors have discovered its potential. XML is showing up everywhere from configu