code: func (t SimpleType) Validate() error {
  	if !t.Kind.IsSimpleType() {
  		return errs.New("a simple type can only have a simple type (e.g. no list or enum)")
  	}
  	_, err := t.SetDefaultValue(t.DefaultValue)
  	if err != nil {
  		return errs.Wrapf(err, "failed to validate default value for kind %s: %+v (%[1]T)", t.Kind, t.DefaultValue)
  	}
  	return nil
  }
docs: // Validate checks that the default value matches the Kind