Representing a dependency, which is basically a version string and a compare methode, e.g. '>=1.0.0 <2.0.0' (i.e. a space separates the two version numbers)
A version in the format "major.update.bugfix-pre-release+build-metadata" or "~master", to identify trunk, or "~branch_name" to identify a branch. Both Version types starting with "~" refer to the head revision of the corresponding branch.
Stuff with dependencies.