rail class not listed under "possible values" for transportation

[fynngodau]

rail is not listed as a possible class value for transportation in the schema. Since I found a railway with the class = subclass = rail using the inspect tool at https://openmaptiles.org/inspect/#13.86/49.7974/9.9361, as seen in the screenshot below, I suspect this to be a bug in the spec.

Whatever the cause, either spec or implementation should be updated to avoid bugs in styles.

[TomPohys]

Thanks for pointing this out. The classes rail and transit are missing in transportation.yaml. The railway_class function should be converted same as highway_class and assign logic should be in transportation.yaml.

PR is very welcome!