So how do we learn XML in general and our shared tag set in specific? That’s harder. People learn by watching others. It is not unlike the old apprentice system, and you can hope you are apprenticed to a master, not a dud.

Learning a tag set and good XML practice is sort of a community values thing, transmitted over discussion lists, at conferences, and through examples. Some, but far from all, introductions to XML and principles of XML design address generic markup, separation of content from formatting, structural markup versus and procedural markup. Some go even further, and talk about separation of concerns at several levels, for example separating the grammar of a document type from local or temporal business rules. But large tag sets are very diverse.