An ASDF system definition can have a :version option. Only one format is supported: one or more integers separated by dots.
These are valid ASDF system versions: "42", "1.8", "2.0.61". These are invalid ASDF system versions: "v1.0", "2.0b", "2004-08-01", "1.0-SNAPSHOT".
If you load a system with an invalid version string, ASDF gives a warning: WARNING: Invalid version "FOO" for component "bar"
If you want to include a version in your ASDF system, please use a valid format. If your software's versioning can't fit into that kind of format, consider putting it in a different field, like :description.