The world of XML is vast and growing, with a huge variety of standards and technologies that interact in complex ways. It can be difficult for beginners to navigate the most important aspects of XML, and for users to keep track of new entries and changes in the space. XML is a basic syntax upon which you develop local and global vocabularies. This index provides a detailed cross-reference of many XML standards, including links to additional coverage for each.
XML started strong and has grown quite rapidly. It has proven itself a valuable technology, but it can be an intimidating one, when one considers all the moving parts that fall under the term "XML." This index of XML standards contains links to a series of articles that provide a summary of key XML technologies. You will also find recommendations of tutorials and other useful resources for evaluating and learning to use each technology.
The word standard is a bit slippery. Standards come in all forms, and multiple standards often compete in the same space. The practical approach is to define a standard as any specification that is significantly adopted by a diversity of vendors or is recommended by a respectable, vendor-neutral organization. This is, of course, a subjective criterion, but this material should give you enough of a start to be able to apply your own judgments on what XML technologies to use.