signature/policy_config.go
func newPRSignedBaseLayer(baseLayerIdentity PolicyReferenceMatch) (*prSignedBaseLayer, error) {
	if baseLayerIdentity == nil {
		return nil, InvalidPolicyFormatError("baseLayerIdentity not specified")
	}
	return &prSignedBaseLayer{
		prCommon:          prCommon{Type: prTypeSignedBaseLayer},
		BaseLayerIdentity: baseLayerIdentity,
	}, nil
}
func newPRSignedBaseLayer(baseLayerIdentity PolicyReferenceMatch) (*prSignedBaseLayer, error) {
	if baseLayerIdentity == nil {
		return nil, InvalidPolicyFormatError("baseLayerIdentity not specified")
	}
	return &prSignedBaseLayer{
		prCommon:          prCommon{Type: prTypeSignedBaseLayer},
		BaseLayerIdentity: baseLayerIdentity,
	}, nil
}
// newPRSignedBaseLayer is NewPRSignedBaseLayer, except it returns the private type.