Features: Input other than enum?

I noticed that the test case set value that are not in the enum.

https://github.com/devcontainers/feature-starter/blob/ea254a2b7d67d8526a6b9c85cfb5d96abfa780b2/test/_global/scenarios.json#L5-L7

https://github.com/devcontainers/feature-starter/blob/ea254a2b7d67d8526a6b9c85cfb5d96abfa780b2/src/color/devcontainer-feature.json#L7-L13

This may work for now, but I don't think it is generally expected behavior to enter any other value for an option that has enum set.