allowedValues property
A list of allowed values for this parameter.
When non-empty, the parameter value must match one of these values.
This is particularly useful for parameters that accept a fixed set of options.
The allowed values must matche the value's toString() method.
If the parameter is not required, the allowed values are only enforced if the parameter is provided.
For example, a "units" parameter might only accept "metric", "imperial".
Implementation
final List<String> allowedValues;