This tcllib package implements a number of common commands used by the validation types in this module. These commands essentially encapsulate the throwing of validation errors, ensuring that a proper -errorcode is used.
AMG: I don't understand the first sentence: "This package implements commands used by this module." That's awfully circular. What's really being said?
AK: I am not sure either. There is no package "valtype". There is a module "valtype", which consists of several packages. One of them, "valtype::common", provides common stuff used by the other packages in said module.