Validation units for specific tags. These validation units combine a set of constraints in order to validate a specific tag (or tag relationship) in a message.

These classes apply a validation to a specific tag. In most cases, a tag with the same name across different MTs will probably have the same constraints, in other words: constraints can be applied to tags regardless of the containing message.

This package offers classes to validate these tags. In this form, validations written for a tag in a given a message can easily be reused.