We use P2 Category Publisher tool to publish category metadata to our p2-repo. And now the features are categorized based on our Products. Now we have a requirement to list sub-level categories based on functionality of features under main feature categories. Is there a way to define sub-categories using category.xml or a work-around to achieve this?
For example in the following sample category.xml  how can I define category c2.1 as a subcategory under c2?
Also Can I give version IDs for my category-defs?