Allowed values for WPS4R

[nuest]

Implement an annotation that can be used to provide allowed values for literal inputs, see class RAttribute.

Possible features:

• a collection of strings, e.g. # wps.in: names, string, allowedValues = Spock, Uhura, Kirk;
• a range for numerical values, e.g. # wps.in: sampleSize, integer, allowedValues = [0,100);

Questions:

• What is the WPS internal API for allowed values? Does it exist?