Starting from Compose* version 0.9.0 a new syntax for concern definitions is used. The old syntax can still be used, internally it will be rewritten to the new syntax.
Proper documentation of the new syntax is currently not available. So for the time being you will have to do it with the annotation reference manual, and the draft for the canonical filter specification.
Note: the draft document does contain some errors and contains information about features that are not (yet) available.
Additional information is also available in the slides of an internal presentation about the Compose* project: