Currently, the default value and custom converter can only be specified at the class level, which is not useful at all for the following reasons:

1. IDefaultValueProvider returns a String, not the actual field type.
2. It is cumbersome to use IDefaultValueProvider to provide default values for multiple fields.
3. Custom converter is useless when the same source type (string) needs to be converted to different target types.

Being able to provide a default value provider class and a converter class in the Option (and Parameter) annotation would be extremely useful. The default value provider may return a type that can be converted to the field type using the available converters (including the inline one).