diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ec66d5c..a0290bc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,6 +30,9 @@ Finally, the `draft` flag has been removed from the header, and much more emphas
 - `pt`: moved SAF-T specific extensions to `addons/pt/saft`.
 - `it`: moved SDI and FatturaPA extensions to `addons/it/sdi` with key `it-sdi-v1`.
 - `gr`: moved MyDATA to `addons/gr/mydata`, key `gr-mydata-v1`.
+- `bill.Preceding`: replaced with `org.DocumentRef`.
+- `bill.Invoice`: Ordering now using arrays of `org.DocumentRef`.
+- `bill.Invoice`: `series` and `code` now use `cbc.Code` and normalization instead of the independent invoice code.
 
 ### Added
 
@@ -39,6 +42,7 @@ Finally, the `draft` flag has been removed from the header, and much more emphas
 - `tax`: `Scenario` now has `Filter` property to set a code function.
 - `tax`: `AddonDef` provides support for defining addon extension packs.
 - `gr`: `gr-mydata-invoice-type` extension with related tags and scenarios.
+- `org`: `DocumentRef` consolidates references to previous documents in a single place.
 
 ## [v0.115.1]
 
diff --git a/addons/es/facturae/invoice.go b/addons/es/facturae/invoice.go
index fe071431..9fc769fb 100644
--- a/addons/es/facturae/invoice.go
+++ b/addons/es/facturae/invoice.go
@@ -3,6 +3,7 @@ package facturae
 import (
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cbc"
+	"github.com/invopop/gobl/org"
 	"github.com/invopop/gobl/regimes/es"
 	"github.com/invopop/gobl/tax"
 	"github.com/invopop/validation"
@@ -57,7 +58,7 @@ func validateInvoiceTax(val any) error {
 }
 
 func validateInvoicePreceding(val any) error {
-	p, ok := val.(*bill.Preceding)
+	p, ok := val.(*org.DocumentRef)
 	if !ok {
 		return nil
 	}
diff --git a/addons/es/facturae/invoice_test.go b/addons/es/facturae/invoice_test.go
index 8e52dd40..f9f679e3 100644
--- a/addons/es/facturae/invoice_test.go
+++ b/addons/es/facturae/invoice_test.go
@@ -31,7 +31,7 @@ func TestInvoicePrecedingValidation(t *testing.T) {
 	err := inv.Validate()
 	assert.ErrorContains(t, err, "preceding: cannot be blank.")
 
-	inv.Preceding = []*bill.Preceding{
+	inv.Preceding = []*org.DocumentRef{
 		{
 			Code: "123TEST",
 		},
diff --git a/addons/es/tbai/invoice.go b/addons/es/tbai/invoice.go
index e9d76acb..875d51a5 100644
--- a/addons/es/tbai/invoice.go
+++ b/addons/es/tbai/invoice.go
@@ -3,6 +3,7 @@ package tbai
 import (
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cbc"
+	"github.com/invopop/gobl/org"
 	"github.com/invopop/gobl/regimes/es"
 	"github.com/invopop/gobl/tax"
 	"github.com/invopop/validation"
@@ -38,7 +39,7 @@ func validateInvoice(inv *bill.Invoice) error {
 }
 
 func validateInvoicePreceding(val any) error {
-	p, ok := val.(*bill.Preceding)
+	p, ok := val.(*org.DocumentRef)
 	if !ok {
 		return nil
 	}
diff --git a/addons/gr/mydata/invoices.go b/addons/gr/mydata/invoices.go
index c5eceaf3..4af7d9f6 100644
--- a/addons/gr/mydata/invoices.go
+++ b/addons/gr/mydata/invoices.go
@@ -58,7 +58,7 @@ func validateInvoice(inv *bill.Invoice) error {
 				inv.Type.In(bill.InvoiceTypeCreditNote),
 				validation.Required,
 			),
-			validation.Each(validation.By(validatePreceding)),
+			validation.Each(validation.By(validateInvoicePreceding)),
 			validation.Skip,
 		),
 	)
@@ -169,8 +169,8 @@ func validateInvoicePayment(value any) error {
 	)
 }
 
-func validatePreceding(value any) error {
-	p, ok := value.(*bill.Preceding)
+func validateInvoicePreceding(value any) error {
+	p, ok := value.(*org.DocumentRef)
 	if !ok || p == nil {
 		return nil
 	}
diff --git a/addons/gr/mydata/invoices_test.go b/addons/gr/mydata/invoices_test.go
index 64e06bd4..9a7c2986 100644
--- a/addons/gr/mydata/invoices_test.go
+++ b/addons/gr/mydata/invoices_test.go
@@ -105,7 +105,7 @@ func TestSimplifiedInvoiceValidation(t *testing.T) {
 func TestPrecedingValidation(t *testing.T) {
 	inv := validInvoice()
 
-	inv.Preceding = []*bill.Preceding{
+	inv.Preceding = []*org.DocumentRef{
 		{
 			Code: "123",
 			Stamps: []*head.Stamp{
diff --git a/addons/mx/cfdi/food_vouchers.go b/addons/mx/cfdi/food_vouchers.go
index 8fcd270b..903cbb61 100644
--- a/addons/mx/cfdi/food_vouchers.go
+++ b/addons/mx/cfdi/food_vouchers.go
@@ -6,7 +6,7 @@ import (
 	"github.com/invopop/gobl/cal"
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/num"
-	"github.com/invopop/gobl/regimes/mx/sat"
+	"github.com/invopop/gobl/regimes/mx"
 	"github.com/invopop/validation"
 )
 
@@ -103,7 +103,7 @@ func (fve *FoodVouchersEmployee) Validate() error {
 	return validation.ValidateStruct(fve,
 		validation.Field(&fve.TaxCode,
 			validation.Required,
-			validation.By(sat.ValidateTaxCode),
+			validation.By(mx.ValidateTaxCode),
 		),
 		validation.Field(&fve.CURP,
 			validation.Required,
diff --git a/addons/mx/cfdi/fuel_account_balance.go b/addons/mx/cfdi/fuel_account_balance.go
index 08a38cf2..4972e6fe 100644
--- a/addons/mx/cfdi/fuel_account_balance.go
+++ b/addons/mx/cfdi/fuel_account_balance.go
@@ -5,7 +5,7 @@ import (
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/num"
 	"github.com/invopop/gobl/org"
-	"github.com/invopop/gobl/regimes/mx/sat"
+	"github.com/invopop/gobl/regimes/mx"
 	"github.com/invopop/gobl/tax"
 	"github.com/invopop/validation"
 )
@@ -19,7 +19,7 @@ const (
 // FuelAccountValidTaxCodes lists of the complement's allowed tax codes
 var FuelAccountValidTaxCodes = []any{
 	tax.CategoryVAT,
-	sat.TaxCategoryIEPS,
+	mx.TaxCategoryIEPS,
 }
 
 // FuelAccountBalance carries the data to produce a CFDI's "Complemento de
@@ -112,7 +112,7 @@ func (fal *FuelAccountLine) Validate() error {
 		validation.Field(&fal.PurchaseDateTime, cal.DateTimeNotZero()),
 		validation.Field(&fal.VendorTaxCode,
 			validation.Required,
-			validation.By(sat.ValidateTaxCode),
+			validation.By(mx.ValidateTaxCode),
 		),
 		validation.Field(&fal.ServiceStationCode,
 			validation.Required,
diff --git a/addons/mx/cfdi/fuel_account_balance_test.go b/addons/mx/cfdi/fuel_account_balance_test.go
index b82e9452..8aea9049 100644
--- a/addons/mx/cfdi/fuel_account_balance_test.go
+++ b/addons/mx/cfdi/fuel_account_balance_test.go
@@ -7,7 +7,7 @@ import (
 
 	"github.com/invopop/gobl/addons/mx/cfdi"
 	"github.com/invopop/gobl/num"
-	"github.com/invopop/gobl/regimes/mx/sat"
+	"github.com/invopop/gobl/regimes/mx"
 	"github.com/invopop/gobl/tax"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -139,7 +139,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(16, 2),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(59195, 4),
 						},
 					},
@@ -153,7 +153,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(16, 2),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(59195, 4),
 						},
 					},
@@ -187,7 +187,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(16, 2),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(5451, 4),
 						},
 					},
@@ -201,7 +201,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(16, 2),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(5451, 4),
 						},
 					},
@@ -250,7 +250,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(int64(vat*1000), 3),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(int64(ieps*10000), 4),
 						},
 					},
@@ -329,7 +329,7 @@ func TestCalculate(t *testing.T) {
 							Percent:  num.NewPercentage(int64(vat*1000), 3),
 						},
 						{
-							Category: sat.TaxCategoryIEPS,
+							Category: mx.TaxCategoryIEPS,
 							Rate:     num.NewAmount(int64(ieps*1000), 3),
 						},
 					},
diff --git a/addons/mx/cfdi/invoice.go b/addons/mx/cfdi/invoice.go
index a32e2a9d..23394650 100644
--- a/addons/mx/cfdi/invoice.go
+++ b/addons/mx/cfdi/invoice.go
@@ -5,7 +5,7 @@ import (
 	"github.com/invopop/gobl/head"
 	"github.com/invopop/gobl/num"
 	"github.com/invopop/gobl/org"
-	"github.com/invopop/gobl/regimes/mx/sat"
+	"github.com/invopop/gobl/regimes/mx"
 	"github.com/invopop/gobl/tax"
 	"github.com/invopop/validation"
 )
@@ -17,27 +17,6 @@ func normalizeInvoice(inv *bill.Invoice) {
 		normalizeItem(line.Item)
 	}
 
-	// 2024-04-26: copy suppliers post code to invoice, if not already
-	// set.
-	if inv.Tax == nil {
-		inv.Tax = new(bill.Tax)
-	}
-	if inv.Tax.Ext == nil {
-		inv.Tax.Ext = make(tax.Extensions)
-	}
-	if inv.Tax.Ext.Has(ExtKeyIssuePlace) {
-		return
-	}
-	if inv.Supplier.Ext.Has(ExtKeyPostCode) {
-		inv.Tax.Ext[ExtKeyIssuePlace] = inv.Supplier.Ext[ExtKeyPostCode]
-		return
-	}
-	if len(inv.Supplier.Addresses) > 0 {
-		addr := inv.Supplier.Addresses[0]
-		if addr.Code != "" {
-			inv.Tax.Ext[ExtKeyIssuePlace] = tax.ExtValue(addr.Code)
-		}
-	}
 }
 
 func validateInvoice(inv *bill.Invoice) error {
@@ -76,7 +55,7 @@ func validateInvoice(inv *bill.Invoice) error {
 	)
 }
 
-func validateInvoiceTax(preceding []*bill.Preceding) validation.RuleFunc {
+func validateInvoiceTax(preceding []*org.DocumentRef) validation.RuleFunc {
 	return func(value any) error {
 		obj, _ := value.(*bill.Tax)
 		if obj == nil {
@@ -156,14 +135,14 @@ func validateInvoiceLine(value any) error {
 }
 
 func validateInvoicePreceding(value interface{}) error {
-	entry, _ := value.(*bill.Preceding)
+	entry, _ := value.(*org.DocumentRef)
 	if entry == nil {
 		return nil
 	}
 	return validation.ValidateStruct(entry,
 		validation.Field(
 			&entry.Stamps,
-			head.StampsHas(sat.StampUUID),
+			head.StampsHas(mx.StampSATUUID),
 			validation.Skip,
 		),
 	)
diff --git a/addons/mx/cfdi/invoice_test.go b/addons/mx/cfdi/invoice_test.go
index 27aa6eee..a8cd80c9 100644
--- a/addons/mx/cfdi/invoice_test.go
+++ b/addons/mx/cfdi/invoice_test.go
@@ -190,7 +190,7 @@ func TestUsoCFDIScenarioValidation(t *testing.T) {
 func TestPrecedingValidation(t *testing.T) {
 	inv := validInvoice()
 
-	inv.Preceding = []*bill.Preceding{
+	inv.Preceding = []*org.DocumentRef{
 		{
 			Code: "123",
 			Stamps: []*head.Stamp{
diff --git a/addons/mx/cfdi/party.go b/addons/mx/cfdi/party.go
index 9c47f84e..51e6ea23 100644
--- a/addons/mx/cfdi/party.go
+++ b/addons/mx/cfdi/party.go
@@ -23,13 +23,4 @@ func normalizeParty(p *org.Party) {
 		}
 	}
 	p.Identities = idents
-
-	// 2024-03-14: Migrate Tax ID Zone to extensions "mx-cfdi-post-code"
-	if p.TaxID != nil && p.TaxID.Zone != "" { //nolint:staticcheck
-		if p.Ext == nil {
-			p.Ext = make(tax.Extensions)
-		}
-		p.Ext[ExtKeyPostCode] = tax.ExtValue(p.TaxID.Zone) //nolint:staticcheck
-		p.TaxID.Zone = ""                                  //nolint:staticcheck
-	}
 }
diff --git a/addons/mx/cfdi/party_test.go b/addons/mx/cfdi/party_test.go
index 67bc7344..1b50cc12 100644
--- a/addons/mx/cfdi/party_test.go
+++ b/addons/mx/cfdi/party_test.go
@@ -22,20 +22,13 @@ func TestMigratePartyIdentities(t *testing.T) {
 				Code: "G01",
 			},
 		},
-		TaxID: &tax.Identity{
-			Country: "MX",
-			Code:    "ZZZ010101ZZZ",
-			Zone:    "65000",
-		},
 	}
 
 	addon := tax.AddonForKey(cfdi.V4)
 	addon.Normalizer(customer)
 
 	assert.Empty(t, customer.Identities)
-	assert.Len(t, customer.Ext, 3)
+	assert.Len(t, customer.Ext, 2)
 	assert.Equal(t, "608", customer.Ext[cfdi.ExtKeyFiscalRegime].String())
 	assert.Equal(t, "G01", customer.Ext[cfdi.ExtKeyUse].String())
-	assert.Equal(t, "65000", customer.Ext[cfdi.ExtKeyPostCode].String())
-	assert.Empty(t, customer.TaxID.Zone) //nolint:staticcheck
 }
diff --git a/addons/mx/cfdi/tax_combo.go b/addons/mx/cfdi/tax_combo.go
index dd71845a..44726734 100644
--- a/addons/mx/cfdi/tax_combo.go
+++ b/addons/mx/cfdi/tax_combo.go
@@ -1,18 +1,18 @@
 package cfdi
 
 import (
-	"github.com/invopop/gobl/regimes/mx/sat"
+	"github.com/invopop/gobl/regimes/mx"
 	"github.com/invopop/gobl/tax"
 )
 
 func normalizeTaxCombo(tc *tax.Combo) {
 	var k tax.ExtValue
 	switch tc.Category {
-	case sat.TaxCategoryISR:
+	case mx.TaxCategoryISR:
 		k = "001"
-	case tax.CategoryVAT, sat.TaxCategoryRVAT:
+	case tax.CategoryVAT, mx.TaxCategoryRVAT:
 		k = "002"
-	case sat.TaxCategoryIEPS, sat.TaxCategoryRIEPS:
+	case mx.TaxCategoryIEPS, mx.TaxCategoryRIEPS:
 		k = "003"
 	default:
 		return
diff --git a/bill/invoice.go b/bill/invoice.go
index 70953592..e7b44cf5 100644
--- a/bill/invoice.go
+++ b/bill/invoice.go
@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"regexp"
 
 	"github.com/invopop/gobl/cal"
 	"github.com/invopop/gobl/cbc"
@@ -31,18 +30,6 @@ const (
 	defaultCurrencyConversionAccuracy uint32 = 2
 )
 
-const (
-	// InvoiceCodePattern defines what we expect from codes
-	// and series in an invoice.
-	InvoiceCodePattern = `^([A-Za-z0-9][A-Za-z0-9 /\._-]?)*[A-Za-z0-9]$`
-)
-
-var (
-	// InvoiceCodeRegexp is used to validate invoice codes and series
-	// to something that is compatible with most tax regimes.
-	InvoiceCodeRegexp = regexp.MustCompile(InvoiceCodePattern)
-)
-
 // Invoice represents a payment claim for goods or services supplied under
 // conditions agreed between the supplier and the customer. In most cases
 // the resulting document describes the actual financial commitment of goods
@@ -57,9 +44,9 @@ type Invoice struct {
 	// Type of invoice document subject to the requirements of the local tax regime.
 	Type cbc.Key `json:"type" jsonschema:"title=Type" jsonschema_extras:"calculated=true"`
 	// Used as a prefix to group codes.
-	Series string `json:"series,omitempty" jsonschema:"title=Series"`
+	Series cbc.Code `json:"series,omitempty" jsonschema:"title=Series"`
 	// Sequential code used to identify this invoice in tax declarations.
-	Code string `json:"code" jsonschema:"title=Code"`
+	Code cbc.Code `json:"code" jsonschema:"title=Code"`
 	// When the invoice was created.
 	IssueDate cal.Date `json:"issue_date" jsonschema:"title=Issue Date" jsonschema_extras:"calculated=true"`
 	// Date when the operation defined by the invoice became effective.
@@ -73,7 +60,7 @@ type Invoice struct {
 
 	// Key information regarding previous invoices and potentially details as to why they
 	// were corrected.
-	Preceding []*Preceding `json:"preceding,omitempty" jsonschema:"title=Preceding Details"`
+	Preceding []*org.DocumentRef `json:"preceding,omitempty" jsonschema:"title=Preceding Details"`
 
 	// Special tax configuration for billing.
 	Tax *Tax `json:"tax,omitempty" jsonschema:"title=Tax"`
@@ -139,11 +126,8 @@ func (inv *Invoice) ValidateWithContext(ctx context.Context) error {
 			validation.Required,
 			isValidInvoiceType,
 		),
-		validation.Field(&inv.Series,
-			validation.Match(InvoiceCodeRegexp),
-		),
+		validation.Field(&inv.Series),
 		validation.Field(&inv.Code,
-			validation.Match(InvoiceCodeRegexp),
 			validation.When(
 				internal.IsSigned(ctx),
 				validation.Required.Error("required to sign invoice"),
@@ -301,6 +285,9 @@ func (inv *Invoice) Normalize(normalizers tax.Normalizers) {
 	if inv.Type == cbc.KeyEmpty {
 		inv.Type = InvoiceTypeStandard
 	}
+	inv.Series = cbc.NormalizeCode(inv.Series)
+	inv.Code = cbc.NormalizeCode(inv.Code)
+
 	normalizers.Each(inv)
 
 	tax.Normalize(normalizers, inv.Tax)
@@ -310,6 +297,7 @@ func (inv *Invoice) Normalize(normalizers tax.Normalizers) {
 	tax.Normalize(normalizers, inv.Lines)
 	tax.Normalize(normalizers, inv.Discounts)
 	tax.Normalize(normalizers, inv.Charges)
+	tax.Normalize(normalizers, inv.Ordering)
 	tax.Normalize(normalizers, inv.Payment)
 }
 
@@ -318,7 +306,7 @@ func (inv *Invoice) normalizers() tax.Normalizers {
 	if r := inv.RegimeDef(); r != nil {
 		normalizers = normalizers.Append(r.Normalizer)
 	}
-	for _, a := range inv.GetAddons() {
+	for _, a := range inv.GetAddonDefs() {
 		normalizers = normalizers.Append(a.Normalizer)
 	}
 	return normalizers
@@ -329,7 +317,7 @@ func (inv *Invoice) supportedTags() []cbc.Key {
 	if r := inv.RegimeDef(); r != nil {
 		ts = ts.Merge(tax.TagSetForSchema(r.Tags, ShortSchemaInvoice))
 	}
-	for _, a := range inv.GetAddons() {
+	for _, a := range inv.GetAddonDefs() {
 		ts = ts.Merge(tax.TagSetForSchema(a.Tags, ShortSchemaInvoice))
 	}
 	return ts.Keys()
@@ -341,7 +329,7 @@ func (inv *Invoice) ValidationContext(ctx context.Context) context.Context {
 	if r := inv.RegimeDef(); r != nil {
 		ctx = r.WithContext(ctx)
 	}
-	for _, a := range inv.GetAddons() {
+	for _, a := range inv.GetAddonDefs() {
 		ctx = a.WithContext(ctx)
 	}
 	return ctx
@@ -602,10 +590,10 @@ func (inv *Invoice) UnmarshalJSON(data []byte) error {
 func (Invoice) JSONSchemaExtend(js *jsonschema.Schema) {
 	props := js.Properties
 	if prop, ok := props.Get("series"); ok {
-		prop.Pattern = InvoiceCodePattern
+		prop.Pattern = cbc.CodePattern
 	}
 	if prop, ok := props.Get("code"); ok {
-		prop.Pattern = InvoiceCodePattern
+		prop.Pattern = cbc.CodePattern
 	}
 	// Extend type list
 	if its, ok := props.Get("type"); ok {
diff --git a/bill/invoice_correct.go b/bill/invoice_correct.go
index 5e996c34..01af9304 100644
--- a/bill/invoice_correct.go
+++ b/bill/invoice_correct.go
@@ -10,8 +10,10 @@ import (
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/data"
 	"github.com/invopop/gobl/head"
+	"github.com/invopop/gobl/org"
 	"github.com/invopop/gobl/schema"
 	"github.com/invopop/gobl/tax"
+	"github.com/invopop/gobl/uuid"
 	"github.com/invopop/jsonschema"
 )
 
@@ -26,7 +28,7 @@ type CorrectionOptions struct {
 	// When the new corrective invoice's issue date should be set to.
 	IssueDate *cal.Date `json:"issue_date,omitempty" jsonschema:"title=Issue Date"`
 	// Series to assign to the new corrective invoice.
-	Series string `json:"series,omitempty" jsonschema:"title=Series"`
+	Series cbc.Code `json:"series,omitempty" jsonschema:"title=Series"`
 	// Stamps of the previous document to include in the preceding data.
 	Stamps []*head.Stamp `json:"stamps,omitempty" jsonschema:"title=Stamps"`
 	// Human readable reason for the corrective operation.
@@ -69,7 +71,7 @@ func WithStamps(stamps []*head.Stamp) schema.Option {
 }
 
 // WithSeries assigns a new series to the corrective document.
-func WithSeries(value string) schema.Option {
+func WithSeries(value cbc.Code) schema.Option {
 	return func(o interface{}) {
 		opts := o.(*CorrectionOptions)
 		opts.Series = value
@@ -265,8 +267,8 @@ func (inv *Invoice) Correct(opts ...schema.Option) error {
 	}
 
 	// Copy and prepare the basic fields
-	pre := &Preceding{
-		UUID:      inv.UUID,
+	pre := &org.DocumentRef{
+		Identify:  uuid.Identify{UUID: inv.UUID},
 		Type:      inv.Type,
 		Series:    inv.Series,
 		Code:      inv.Code,
@@ -292,7 +294,7 @@ func (inv *Invoice) Correct(opts ...schema.Option) error {
 	}
 
 	// Replace all previous preceding data
-	inv.Preceding = []*Preceding{pre}
+	inv.Preceding = []*org.DocumentRef{pre}
 
 	// Running a Calculate feels a bit out of place, but not performing
 	// this operation on the corrected invoice results in potentially
@@ -312,7 +314,7 @@ func (inv *Invoice) correctionDef() *tax.CorrectionDefinition {
 	if r != nil {
 		cd = cd.Merge(r.Corrections.Def(ShortSchemaInvoice))
 	}
-	for _, a := range inv.GetAddons() {
+	for _, a := range inv.GetAddonDefs() {
 		cd = cd.Merge(a.Corrections.Def(ShortSchemaInvoice))
 	}
 
@@ -343,7 +345,7 @@ func prepareCorrectionOptions(o *CorrectionOptions, opts ...schema.Option) error
 	return nil
 }
 
-func (inv *Invoice) validatePrecedingData(o *CorrectionOptions, cd *tax.CorrectionDefinition, pre *Preceding) error {
+func (inv *Invoice) validatePrecedingData(o *CorrectionOptions, cd *tax.CorrectionDefinition, pre *org.DocumentRef) error {
 	if cd == nil {
 		return nil
 	}
diff --git a/bill/invoice_correct_test.go b/bill/invoice_correct_test.go
index d10da827..7e936b5e 100644
--- a/bill/invoice_correct_test.go
+++ b/bill/invoice_correct_test.go
@@ -8,6 +8,7 @@ import (
 	"github.com/invopop/gobl/addons/es/tbai"
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/head"
 	"github.com/invopop/gobl/num"
 	"github.com/invopop/gobl/org"
@@ -34,11 +35,11 @@ func TestInvoiceCorrect(t *testing.T) {
 	assert.Equal(t, bill.InvoiceTypeCreditNote, i.Type)
 	assert.Equal(t, i.Lines[0].Quantity.String(), "10")
 	assert.Equal(t, i.IssueDate, cal.Today())
-	assert.Equal(t, i.Series, "TEST")
+	assert.Equal(t, i.Series, cbc.Code("TEST"))
 	assert.Empty(t, i.Code)
 	pre := i.Preceding[0]
-	assert.Equal(t, pre.Series, "TEST")
-	assert.Equal(t, pre.Code, "123")
+	assert.Equal(t, pre.Series.String(), "TEST")
+	assert.Equal(t, pre.Code.String(), "123")
 	assert.Equal(t, pre.IssueDate, cal.NewDate(2022, 6, 13))
 	assert.Equal(t, pre.Reason, "test refund")
 	assert.Equal(t, i.Totals.Payable.String(), "900.00")
@@ -81,8 +82,8 @@ func TestInvoiceCorrect(t *testing.T) {
 		inv := testInvoiceESForCorrection(t)
 		err := inv.Correct(bill.Credit, bill.WithSeries("R-TEST"))
 		require.NoError(t, err)
-		assert.Equal(t, inv.Series, "R-TEST")
-		assert.Equal(t, inv.Preceding[0].Series, "TEST")
+		assert.Equal(t, inv.Series, cbc.Code("R-TEST"))
+		assert.Equal(t, inv.Preceding[0].Series.String(), "TEST")
 	})
 
 	// France case (both corrective and credit note)
@@ -149,11 +150,11 @@ func TestCorrectWithOptions(t *testing.T) {
 	assert.Equal(t, bill.InvoiceTypeCreditNote, i.Type)
 	assert.Equal(t, i.Lines[0].Quantity.String(), "10")
 	assert.Equal(t, i.IssueDate, cal.Today())
-	assert.Equal(t, i.Series, "R-TEST")
+	assert.Equal(t, i.Series.String(), "R-TEST")
 	assert.Empty(t, i.Code)
 	pre := i.Preceding[0]
-	assert.Equal(t, pre.Series, "TEST")
-	assert.Equal(t, pre.Code, "123")
+	assert.Equal(t, pre.Series.String(), "TEST")
+	assert.Equal(t, pre.Code.String(), "123")
 	assert.Equal(t, pre.IssueDate, cal.NewDate(2022, 6, 13))
 	assert.Equal(t, pre.Reason, "test refund")
 	assert.Equal(t, pre.Ext[facturae.ExtKeyCorrection], tax.ExtValue("01"))
diff --git a/bill/invoice_scenarios.go b/bill/invoice_scenarios.go
index 404f2f32..dddd3f50 100644
--- a/bill/invoice_scenarios.go
+++ b/bill/invoice_scenarios.go
@@ -43,7 +43,7 @@ func (inv *Invoice) scenarioSummary() *tax.ScenarioSummary {
 	if r := inv.RegimeDef(); r != nil {
 		ss.Merge(r.Scenarios)
 	}
-	for _, a := range inv.GetAddons() {
+	for _, a := range inv.GetAddonDefs() {
 		ss.Merge(a.Scenarios)
 	}
 
diff --git a/bill/invoice_test.go b/bill/invoice_test.go
index 5335fe8f..82d12560 100644
--- a/bill/invoice_test.go
+++ b/bill/invoice_test.go
@@ -9,6 +9,7 @@ import (
 	_ "github.com/invopop/gobl" // load regions
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/currency"
 	"github.com/invopop/gobl/internal"
 	"github.com/invopop/gobl/l10n"
@@ -20,34 +21,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestInvoiceCodeRegexp(t *testing.T) {
-	tests := []struct {
-		code string
-		ok   bool
-	}{
-		// Good
-		{"1", true},
-		{"A", true},
-		{"123", true},
-		{"123TEST", true},
-		{"123-TEST", true},
-		{"FR F-01/37", true},
-		{"MultiCase", true},
-		{"F.01_21", true},
-		// Bad
-		{"F101-", false},
-		{" 123 ", false},
-		{"F--01", false},
-		{"\n", false},
-		{"FOO\n", false},
-	}
-	for _, ts := range tests {
-		t.Run(ts.code, func(t *testing.T) {
-			assert.Equal(t, ts.ok, bill.InvoiceCodeRegexp.MatchString(ts.code))
-		})
-	}
-}
-
 func TestInvoiceRegimeCurrency(t *testing.T) {
 	lines := []*bill.Line{
 		{
@@ -1074,6 +1047,15 @@ func TestInvoiceForUnknownRegime(t *testing.T) {
 	require.NoError(t, inv.Validate())
 }
 
+func TestNormalization(t *testing.T) {
+	inv := baseInvoiceWithLines(t)
+	inv.Series = " bar 2024 "
+	inv.Code = " 123 Test "
+	require.NoError(t, inv.Calculate())
+	assert.Equal(t, cbc.Code("BAR-2024"), inv.Series)
+	assert.Equal(t, cbc.Code("123-TEST"), inv.Code)
+}
+
 func TestValidation(t *testing.T) {
 	t.Run("basic validation", func(t *testing.T) {
 		inv := baseInvoiceWithLines(t)
diff --git a/bill/ordering.go b/bill/ordering.go
index 01bbd74c..558c0620 100644
--- a/bill/ordering.go
+++ b/bill/ordering.go
@@ -2,67 +2,73 @@ package bill
 
 import (
 	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/org"
-	"github.com/invopop/gobl/uuid"
+	"github.com/invopop/gobl/tax"
 	"github.com/invopop/validation"
-	"github.com/invopop/validation/is"
 )
 
 // Ordering provides additional information about the ordering process including references
 // to other documents and alternative parties involved in the order-to-delivery process.
 type Ordering struct {
 	// Identifier assigned by the customer or buyer for internal routing purposes.
-	Code string `json:"code,omitempty" jsonschema:"title=Code"`
+	Code cbc.Code `json:"code,omitempty" jsonschema:"title=Code"`
 	// Any additional Codes, IDs, SKUs, or other regional or custom
 	// identifiers that may be used to identify the order.
 	Identities []*org.Identity `json:"identities,omitempty" jsonschema:"title=Identities"`
-
 	// Period of time that the invoice document refers to often used in addition to the details
 	// provided in the individual line items.
 	Period *cal.Period `json:"period,omitempty" jsonschema:"title=Period"`
-	// Project this invoice refers to.
-	Project *DocumentReference `json:"project,omitempty" jsonschema:"title=Project"`
-	// The identification of a contract.
-	Contract *DocumentReference `json:"contract,omitempty" jsonschema:"title=Contract"`
-	// Purchase order issued by the customer or buyer.
-	Purchase *DocumentReference `json:"purchase,omitempty" jsonschema:"title=Purchase Order"`
-	// Sales order issued by the supplier or seller.
-	Sale *DocumentReference `json:"sale,omitempty" jsonschema:"title=Sales Order"`
-	// Receiving Advice.
-	Receiving *DocumentReference `json:"receiving,omitempty" jsonschema:"title=Receiving Advice"`
-	// Despatch advice.
-	Despatch *DocumentReference `json:"despatch,omitempty" jsonschema:"title=Despatch Advice"`
-	// Tender advice, the identification of the call for tender or lot the invoice relates to.
-	Tender *DocumentReference `json:"tender,omitempty" jsonschema:"title=Tender Advice"`
-
 	// Party who is responsible for making the purchase, but is not responsible
 	// for handling taxes.
 	Buyer *org.Party `json:"buyer,omitempty" jsonschema:"title=Buyer"`
 	// Party who is selling the goods but is not responsible for taxes like the
 	// supplier.
 	Seller *org.Party `json:"seller,omitempty" jsonschema:"title=Seller"`
+	// Projects this invoice refers to.
+	Projects []*org.DocumentRef `json:"projects,omitempty" jsonschema:"title=Projects"`
+	// The identification of contracts.
+	Contracts []*org.DocumentRef `json:"contracts,omitempty" jsonschema:"title=Contracts"`
+	// Purchase orders issued by the customer or buyer.
+	Purchases []*org.DocumentRef `json:"purchases,omitempty" jsonschema:"title=Purchase Orders"`
+	// Sales orders issued by the supplier or seller.
+	Sales []*org.DocumentRef `json:"sales,omitempty" jsonschema:"title=Sales Orders"`
+	// Receiving Advice.
+	Receiving []*org.DocumentRef `json:"receiving,omitempty" jsonschema:"title=Receiving Advice"`
+	// Despatch advice.
+	Despatch []*org.DocumentRef `json:"despatch,omitempty" jsonschema:"title=Despatch Advice"`
+	// Tender advice, the identification of the call for tender or lot the invoice relates to.
+	Tender []*org.DocumentRef `json:"tender,omitempty" jsonschema:"title=Tender Advice"`
 }
 
-// DocumentReference provides a link to a existing document.
-type DocumentReference struct {
-	// Unique ID copied from the source document.
-	UUID uuid.UUID `json:"uuid,omitempty" jsonschema:"title=UUID"`
-	// Series the reference document belongs to.
-	Series string `json:"series,omitempty" jsonschema:"title=Series"`
-	// Source document's code or other identifier.
-	Code string `json:"code,omitempty" jsonschema:"title=Code"`
-	// Link to the source document.
-	URL string `json:"url,omitempty" jsonschema:"title=URL,format=uri"`
+// Normalize attempts to clean and normalize the Ordering data.
+func (o *Ordering) Normalize(normalizers tax.Normalizers) {
+	if o == nil {
+		return
+	}
+	o.Code = cbc.NormalizeCode(o.Code)
+	normalizers.Each(o)
+	tax.Normalize(normalizers, o.Identities)
+	tax.Normalize(normalizers, o.Projects)
+	tax.Normalize(normalizers, o.Contracts)
+	tax.Normalize(normalizers, o.Purchases)
+	tax.Normalize(normalizers, o.Sales)
+	tax.Normalize(normalizers, o.Receiving)
+	tax.Normalize(normalizers, o.Despatch)
+	tax.Normalize(normalizers, o.Tender)
+	tax.Normalize(normalizers, o.Buyer)
+	tax.Normalize(normalizers, o.Seller)
 }
 
 // Validate the ordering details.
 func (o *Ordering) Validate() error {
 	return validation.ValidateStruct(o,
+		validation.Field(&o.Code),
 		validation.Field(&o.Identities),
-		validation.Field(&o.Project),
-		validation.Field(&o.Contract),
-		validation.Field(&o.Purchase),
-		validation.Field(&o.Sale),
+		validation.Field(&o.Projects),
+		validation.Field(&o.Contracts),
+		validation.Field(&o.Purchases),
+		validation.Field(&o.Sales),
 		validation.Field(&o.Receiving),
 		validation.Field(&o.Despatch),
 		validation.Field(&o.Tender),
@@ -70,14 +76,3 @@ func (o *Ordering) Validate() error {
 		validation.Field(&o.Seller),
 	)
 }
-
-// Validate ensures the Document Reference looks correct.
-func (dr *DocumentReference) Validate() error {
-	return validation.ValidateStruct(dr,
-		validation.Field(&dr.UUID),
-		validation.Field(&dr.Code,
-			validation.Match(InvoiceCodeRegexp),
-		),
-		validation.Field(&dr.URL, is.URL),
-	)
-}
diff --git a/bill/ordering_test.go b/bill/ordering_test.go
new file mode 100644
index 00000000..2384bc18
--- /dev/null
+++ b/bill/ordering_test.go
@@ -0,0 +1,42 @@
+package bill_test
+
+import (
+	"testing"
+
+	"github.com/invopop/gobl/bill"
+	"github.com/invopop/gobl/org"
+	"github.com/invopop/gobl/tax"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestOrderingNormalize(t *testing.T) {
+	o := &bill.Ordering{
+		Code: " Foo ",
+		Projects: []*org.DocumentRef{
+			{
+				Code: " Bar ",
+				Ext: tax.Extensions{
+					"missing": "",
+				},
+			},
+		},
+	}
+	o.Normalize(nil)
+	assert.Equal(t, "FOO", o.Code.String())
+	assert.Equal(t, "BAR", o.Projects[0].Code.String())
+	assert.Empty(t, o.Projects[0].Ext)
+}
+
+func TestOrderingValidate(t *testing.T) {
+	o := &bill.Ordering{
+		Code: "123",
+	}
+	err := o.Validate()
+	assert.NoError(t, err)
+
+	o.Projects = []*org.DocumentRef{
+		{},
+	}
+	err = o.Validate()
+	assert.ErrorContains(t, err, "projects: (0: (code: cannot be blank.).)")
+}
diff --git a/bill/preceding.go b/bill/preceding.go
deleted file mode 100644
index eebc2a51..00000000
--- a/bill/preceding.go
+++ /dev/null
@@ -1,91 +0,0 @@
-package bill
-
-import (
-	"context"
-
-	"github.com/invopop/gobl/cal"
-	"github.com/invopop/gobl/cbc"
-	"github.com/invopop/gobl/head"
-	"github.com/invopop/gobl/tax"
-	"github.com/invopop/gobl/uuid"
-	"github.com/invopop/jsonschema"
-	"github.com/invopop/validation"
-)
-
-// Preceding allows for information to be provided about a previous invoice that this one
-// will replace, subtract from, or add to. If this is used, the invoice type code will most likely need
-// to be set to `corrective`, `credit-note`, or similar.
-type Preceding struct {
-	// Preceding document's UUID.
-	UUID uuid.UUID `json:"uuid,omitempty" jsonschema:"title=UUID"`
-	// Type of the preceding document
-	Type cbc.Key `json:"type,omitempty" jsonschema:"title=Type"`
-	// Series identification code
-	Series string `json:"series,omitempty" jsonschema:"title=Series"`
-	// Code of the previous document.
-	Code string `json:"code" jsonschema:"title=Code"`
-	// The issue date of the previous document.
-	IssueDate *cal.Date `json:"issue_date,omitempty" jsonschema:"title=Issue Date"`
-	// Human readable description on why the preceding invoice is being replaced.
-	Reason string `json:"reason,omitempty" jsonschema:"title=Reason"`
-	// Seals of approval from other organisations that may need to be listed.
-	Stamps []*head.Stamp `json:"stamps,omitempty" jsonschema:"title=Stamps"`
-	// Tax period in which the previous invoice had an effect required by some tax regimes and formats.
-	Period *cal.Period `json:"period,omitempty" jsonschema:"title=Period"`
-	// Extensions for region specific requirements.
-	Ext tax.Extensions `json:"ext,omitempty" jsonschema:"title=Extensions"`
-	// Additional semi-structured data that may be useful in specific regions
-	Meta cbc.Meta `json:"meta,omitempty" jsonschema:"title=Meta"`
-}
-
-// Validate ensures the preceding details look okay
-func (p *Preceding) Validate() error {
-	return p.ValidateWithContext(context.Background())
-}
-
-// Normalize tries to normalize the preceding data.
-func (p *Preceding) Normalize(normalizers tax.Normalizers) {
-	if p == nil {
-		return
-	}
-	p.Stamps = head.NormalizeStamps(p.Stamps)
-	p.Ext = tax.CleanExtensions(p.Ext)
-	normalizers.Each(p)
-}
-
-// ValidateWithContext ensures the preceding details look okay
-func (p *Preceding) ValidateWithContext(ctx context.Context) error {
-	return validation.ValidateStructWithContext(ctx, p,
-		validation.Field(&p.UUID),
-		validation.Field(&p.Type),
-		validation.Field(&p.Series),
-		validation.Field(&p.Code, validation.Required),
-		validation.Field(&p.IssueDate, cal.DateNotZero()),
-		validation.Field(&p.Stamps),
-		validation.Field(&p.Period),
-		validation.Field(&p.Ext),
-		validation.Field(&p.Meta),
-	)
-}
-
-// JSONSchemaExtend extends the schema with additional property details
-func (Preceding) JSONSchemaExtend(schema *jsonschema.Schema) {
-	props := schema.Properties
-	if prop, ok := props.Get("series"); ok {
-		prop.Pattern = InvoiceCodePattern
-	}
-	if prop, ok := props.Get("code"); ok {
-		prop.Pattern = InvoiceCodePattern
-	}
-	// Extend type list
-	if its, ok := props.Get("type"); ok {
-		its.OneOf = make([]*jsonschema.Schema, len(InvoiceTypes))
-		for i, kd := range InvoiceTypes {
-			its.OneOf[i] = &jsonschema.Schema{
-				Const:       kd.Key.String(),
-				Title:       kd.Name.String(),
-				Description: kd.Desc.String(),
-			}
-		}
-	}
-}
diff --git a/bill/preceding_test.go b/bill/preceding_test.go
deleted file mode 100644
index 74471d03..00000000
--- a/bill/preceding_test.go
+++ /dev/null
@@ -1,18 +0,0 @@
-package bill_test
-
-import (
-	"testing"
-
-	"github.com/invopop/gobl/bill"
-	"github.com/invopop/gobl/cal"
-	"github.com/stretchr/testify/assert"
-)
-
-func TestPrecedingValidation(t *testing.T) {
-	p := new(bill.Preceding)
-	p.Code = "FOO"
-	p.IssueDate = cal.NewDate(2022, 11, 6)
-
-	err := p.Validate()
-	assert.NoError(t, err)
-}
diff --git a/cbc/code.go b/cbc/code.go
index deccccf9..b1c4f631 100644
--- a/cbc/code.go
+++ b/cbc/code.go
@@ -3,6 +3,7 @@ package cbc
 import (
 	"errors"
 	"regexp"
+	"strings"
 
 	"github.com/invopop/jsonschema"
 	"github.com/invopop/validation"
@@ -12,7 +13,7 @@ import (
 // at. We use "code" instead of "id", to reenforce the fact that codes should
 // be more easily set and used by humans within definitions than IDs or UUIDs.
 // Codes are standardised so that when validated they must contain between
-// 1 and 24 inclusive upper-case letters or numbers with optional periods (`.`),
+// 1 and 32 inclusive upper-case letters or numbers with optional periods (`.`),
 // dashes (`-`), or forward slashes (`/`) to separate blocks.
 type Code string
 
@@ -22,23 +23,35 @@ type CodeMap map[Key]Code
 
 // Basic code constants.
 var (
-	CodePattern          = `^[A-Z0-9]+([\.\-\/]?[A-Z0-9]+)*$`
-	CodeMinLength uint64 = 1
-	CodeMaxLength uint64 = 24
+	CodePattern              = `^[A-Z0-9]+([\.\-\/]?[A-Z0-9]+)*$`
+	CodePatternRegexp        = regexp.MustCompile(CodePattern)
+	CodeMinLength     uint64 = 1
+	CodeMaxLength     uint64 = 32
 )
 
 var (
-	codeValidationRegexp = regexp.MustCompile(CodePattern)
+	codeUnderscoreOrSpaceRegexp = regexp.MustCompile(`[_ ]`)
+	codeInvalidCharsRegexp      = regexp.MustCompile(`[^A-Z0-9\.\-\/]`)
 )
 
 // CodeEmpty is used when no code is defined.
 const CodeEmpty Code = ""
 
+// NormalizeCode attempts to clean and normalize the provided code so that
+// it matches what we'd expect instead of raising validation errors.
+func NormalizeCode(c Code) Code {
+	code := strings.ToUpper(c.String())
+	code = strings.TrimSpace(code)
+	code = codeUnderscoreOrSpaceRegexp.ReplaceAllString(code, "-")
+	code = codeInvalidCharsRegexp.ReplaceAllString(code, "")
+	return Code(code)
+}
+
 // Validate ensures that the code complies with the expected rules.
 func (c Code) Validate() error {
 	return validation.Validate(string(c),
 		validation.Length(1, int(CodeMaxLength)),
-		validation.Match(codeValidationRegexp),
+		validation.Match(CodePatternRegexp),
 	)
 }
 
diff --git a/cbc/code_test.go b/cbc/code_test.go
index 10271114..8a97433a 100644
--- a/cbc/code_test.go
+++ b/cbc/code_test.go
@@ -14,6 +14,66 @@ func TestCodeIn(t *testing.T) {
 	assert.False(t, c.In("BAR", "DOM"))
 }
 
+func TestNormalizeCode(t *testing.T) {
+	tests := []struct {
+		name string
+		code cbc.Code
+		want cbc.Code
+	}{
+		{
+			name: "uppercase",
+			code: cbc.Code("FOO"),
+			want: cbc.Code("FOO"),
+		},
+		{
+			name: "lowercase",
+			code: cbc.Code("foo"),
+			want: cbc.Code("FOO"),
+		},
+		{
+			name: "mixed case",
+			code: cbc.Code("Foo"),
+			want: cbc.Code("FOO"),
+		},
+		{
+			name: "with spaces",
+			code: cbc.Code("FOO BAR"),
+			want: cbc.Code("FOO-BAR"),
+		},
+		{
+			name: "empty",
+			code: cbc.Code(""),
+			want: cbc.Code(""),
+		},
+		{
+			name: "underscore",
+			code: cbc.Code("FOO_BAR"),
+			want: cbc.Code("FOO-BAR"),
+		},
+		{
+			name: "whitespace",
+			code: cbc.Code(" foo-bar1  "),
+			want: cbc.Code("FOO-BAR1"),
+		},
+		{
+			name: "invalid chars",
+			code: cbc.Code("f$oo-bar1!"),
+			want: cbc.Code("FOO-BAR1"),
+		},
+		{
+			name: "multiple spaces",
+			code: cbc.Code("foo bar dome"),
+			want: cbc.Code("FOO-BAR-DOME"),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, cbc.NormalizeCode(tt.code))
+		})
+	}
+
+}
+
 func TestCode_Validate(t *testing.T) {
 	tests := []struct {
 		name    string
@@ -52,6 +112,10 @@ func TestCode_Validate(t *testing.T) {
 			name: "empty",
 			code: cbc.Code(""),
 		},
+		{
+			name: "almost too long",
+			code: cbc.Code("123456789012345678901234567890AB"),
+		},
 		{
 			name:    "dot at start",
 			code:    cbc.Code(".B123"),
@@ -82,9 +146,24 @@ func TestCode_Validate(t *testing.T) {
 			code:    cbc.Code("AB/.CD"),
 			wantErr: "valid format",
 		},
+		{
+			name:    "character return",
+			code:    cbc.Code("AB\nCD"),
+			wantErr: "valid format",
+		},
+		{
+			name:    "character return",
+			code:    cbc.Code("\n"),
+			wantErr: "valid format",
+		},
+		{
+			name:    "multi-dash",
+			code:    cbc.Code("AB--CD"),
+			wantErr: "valid format",
+		},
 		{
 			name:    "too long",
-			code:    cbc.Code("12345678901234567890ABCDE"),
+			code:    cbc.Code("123456789012345678901234567890ABC"),
 			wantErr: "length must be between",
 		},
 	}
diff --git a/data/schemas/bill/invoice.json b/data/schemas/bill/invoice.json
index f1138515..9de7e2a7 100644
--- a/data/schemas/bill/invoice.json
+++ b/data/schemas/bill/invoice.json
@@ -168,34 +168,6 @@
       ],
       "description": "Discount represents an allowance applied to the complete document independent from the individual lines."
     },
-    "DocumentReference": {
-      "properties": {
-        "uuid": {
-          "type": "string",
-          "format": "uuid",
-          "title": "UUID",
-          "description": "Unique ID copied from the source document."
-        },
-        "series": {
-          "type": "string",
-          "title": "Series",
-          "description": "Series the reference document belongs to."
-        },
-        "code": {
-          "type": "string",
-          "title": "Code",
-          "description": "Source document's code or other identifier."
-        },
-        "url": {
-          "type": "string",
-          "format": "uri",
-          "title": "URL",
-          "description": "Link to the source document."
-        }
-      },
-      "type": "object",
-      "description": "DocumentReference provides a link to a existing document."
-    },
     "Invoice": {
       "properties": {
         "$regime": {
@@ -301,7 +273,7 @@
         },
         "preceding": {
           "items": {
-            "$ref": "#/$defs/Preceding"
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
           },
           "type": "array",
           "title": "Preceding Details",
@@ -567,50 +539,71 @@
           "title": "Period",
           "description": "Period of time that the invoice document refers to often used in addition to the details\nprovided in the individual line items."
         },
-        "project": {
-          "$ref": "#/$defs/DocumentReference",
-          "title": "Project",
-          "description": "Project this invoice refers to."
+        "buyer": {
+          "$ref": "https://gobl.org/draft-0/org/party",
+          "title": "Buyer",
+          "description": "Party who is responsible for making the purchase, but is not responsible\nfor handling taxes."
         },
-        "contract": {
-          "$ref": "#/$defs/DocumentReference",
-          "title": "Contract",
-          "description": "The identification of a contract."
+        "seller": {
+          "$ref": "https://gobl.org/draft-0/org/party",
+          "title": "Seller",
+          "description": "Party who is selling the goods but is not responsible for taxes like the\nsupplier."
+        },
+        "projects": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
+          "title": "Projects",
+          "description": "Projects this invoice refers to."
+        },
+        "contracts": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
+          "title": "Contracts",
+          "description": "The identification of contracts."
         },
-        "purchase": {
-          "$ref": "#/$defs/DocumentReference",
-          "title": "Purchase Order",
-          "description": "Purchase order issued by the customer or buyer."
+        "purchases": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
+          "title": "Purchase Orders",
+          "description": "Purchase orders issued by the customer or buyer."
         },
-        "sale": {
-          "$ref": "#/$defs/DocumentReference",
-          "title": "Sales Order",
-          "description": "Sales order issued by the supplier or seller."
+        "sales": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
+          "title": "Sales Orders",
+          "description": "Sales orders issued by the supplier or seller."
         },
         "receiving": {
-          "$ref": "#/$defs/DocumentReference",
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
           "title": "Receiving Advice",
           "description": "Receiving Advice."
         },
         "despatch": {
-          "$ref": "#/$defs/DocumentReference",
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
           "title": "Despatch Advice",
           "description": "Despatch advice."
         },
         "tender": {
-          "$ref": "#/$defs/DocumentReference",
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/document-ref"
+          },
+          "type": "array",
           "title": "Tender Advice",
           "description": "Tender advice, the identification of the call for tender or lot the invoice relates to."
-        },
-        "buyer": {
-          "$ref": "https://gobl.org/draft-0/org/party",
-          "title": "Buyer",
-          "description": "Party who is responsible for making the purchase, but is not responsible\nfor handling taxes."
-        },
-        "seller": {
-          "$ref": "https://gobl.org/draft-0/org/party",
-          "title": "Seller",
-          "description": "Party who is selling the goods but is not responsible for taxes like the\nsupplier."
         }
       },
       "type": "object",
@@ -698,98 +691,6 @@
       "type": "object",
       "description": "Payment contains details as to how the invoice should be paid."
     },
-    "Preceding": {
-      "properties": {
-        "uuid": {
-          "type": "string",
-          "format": "uuid",
-          "title": "UUID",
-          "description": "Preceding document's UUID."
-        },
-        "type": {
-          "$ref": "https://gobl.org/draft-0/cbc/key",
-          "oneOf": [
-            {
-              "const": "standard",
-              "title": "Standard",
-              "description": "A regular commercial invoice document between a supplier and customer."
-            },
-            {
-              "const": "proforma",
-              "title": "Proforma",
-              "description": "For a clients validation before sending a final invoice."
-            },
-            {
-              "const": "corrective",
-              "title": "Corrective",
-              "description": "Corrected invoice that completely *replaces* the preceding document."
-            },
-            {
-              "const": "credit-note",
-              "title": "Credit Note",
-              "description": "Reflects a refund either partial or complete of the preceding document. A \ncredit note effectively *extends* the previous document."
-            },
-            {
-              "const": "debit-note",
-              "title": "Debit Note",
-              "description": "An additional set of charges to be added to the preceding document."
-            }
-          ],
-          "title": "Type",
-          "description": "Type of the preceding document"
-        },
-        "series": {
-          "type": "string",
-          "pattern": "^([A-Za-z0-9][A-Za-z0-9 /\\._-]?)*[A-Za-z0-9]$",
-          "title": "Series",
-          "description": "Series identification code"
-        },
-        "code": {
-          "type": "string",
-          "pattern": "^([A-Za-z0-9][A-Za-z0-9 /\\._-]?)*[A-Za-z0-9]$",
-          "title": "Code",
-          "description": "Code of the previous document."
-        },
-        "issue_date": {
-          "$ref": "https://gobl.org/draft-0/cal/date",
-          "title": "Issue Date",
-          "description": "The issue date of the previous document."
-        },
-        "reason": {
-          "type": "string",
-          "title": "Reason",
-          "description": "Human readable description on why the preceding invoice is being replaced."
-        },
-        "stamps": {
-          "items": {
-            "$ref": "https://gobl.org/draft-0/head/stamp"
-          },
-          "type": "array",
-          "title": "Stamps",
-          "description": "Seals of approval from other organisations that may need to be listed."
-        },
-        "period": {
-          "$ref": "https://gobl.org/draft-0/cal/period",
-          "title": "Period",
-          "description": "Tax period in which the previous invoice had an effect required by some tax regimes and formats."
-        },
-        "ext": {
-          "$ref": "https://gobl.org/draft-0/tax/extensions",
-          "title": "Extensions",
-          "description": "Extensions for region specific requirements."
-        },
-        "meta": {
-          "$ref": "https://gobl.org/draft-0/cbc/meta",
-          "title": "Meta",
-          "description": "Additional semi-structured data that may be useful in specific regions"
-        }
-      },
-      "type": "object",
-      "required": [
-        "code"
-      ],
-      "description": "Preceding allows for information to be provided about a previous invoice that this one will replace, subtract from, or add to."
-    },
     "Tax": {
       "properties": {
         "prices_include": {
diff --git a/data/schemas/org/document-ref.json b/data/schemas/org/document-ref.json
new file mode 100644
index 00000000..cbdfffc3
--- /dev/null
+++ b/data/schemas/org/document-ref.json
@@ -0,0 +1,95 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://gobl.org/draft-0/org/document-ref",
+  "$ref": "#/$defs/DocumentRef",
+  "$defs": {
+    "DocumentRef": {
+      "properties": {
+        "uuid": {
+          "type": "string",
+          "format": "uuid",
+          "title": "UUID",
+          "description": "Universally Unique Identifier."
+        },
+        "type": {
+          "$ref": "https://gobl.org/draft-0/cbc/key",
+          "title": "Type",
+          "description": "Type of the document referenced."
+        },
+        "issue_date": {
+          "$ref": "https://gobl.org/draft-0/cal/date",
+          "title": "Issue Date",
+          "description": "IssueDate reflects the date the document was issued."
+        },
+        "series": {
+          "$ref": "https://gobl.org/draft-0/cbc/code",
+          "pattern": "^[A-Z0-9]+([\\.\\-\\/]?[A-Z0-9]+)*$",
+          "title": "Series",
+          "description": "Series the referenced document belongs to."
+        },
+        "code": {
+          "$ref": "https://gobl.org/draft-0/cbc/code",
+          "pattern": "^[A-Z0-9]+([\\.\\-\\/]?[A-Z0-9]+)*$",
+          "title": "Code",
+          "description": "Source document's code or other identifier."
+        },
+        "line": {
+          "type": "integer",
+          "title": "Line",
+          "description": "Line index number inside the document, if relevant."
+        },
+        "identities": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/org/identity"
+          },
+          "type": "array",
+          "title": "Identities",
+          "description": "List of additional codes, IDs, or SKUs which can be used to identify the document or its contents, agreed upon by the supplier and customer."
+        },
+        "period": {
+          "$ref": "https://gobl.org/draft-0/cal/period",
+          "title": "Period",
+          "description": "Tax period in which the referred document had an effect required by some tax regimes and formats."
+        },
+        "reason": {
+          "type": "string",
+          "title": "Reason",
+          "description": "Human readable description on why this reference is here or needs to be used."
+        },
+        "description": {
+          "type": "string",
+          "title": "Description",
+          "description": "Additional details about the document."
+        },
+        "stamps": {
+          "items": {
+            "$ref": "https://gobl.org/draft-0/head/stamp"
+          },
+          "type": "array",
+          "title": "Stamps",
+          "description": "Seals of approval from other organisations that may need to be listed."
+        },
+        "url": {
+          "type": "string",
+          "format": "uri",
+          "title": "URL",
+          "description": "Link to the source document."
+        },
+        "ext": {
+          "$ref": "https://gobl.org/draft-0/tax/extensions",
+          "description": "Extensions for additional codes that may be required."
+        },
+        "meta": {
+          "$ref": "https://gobl.org/draft-0/cbc/meta",
+          "title": "Meta",
+          "description": "Meta contains additional information about the document."
+        }
+      },
+      "type": "object",
+      "required": [
+        "code"
+      ],
+      "description": "DocumentRef is used to describe an existing document or a specific part of it's contents."
+    }
+  }
+}
\ No newline at end of file
diff --git a/envelope_test.go b/envelope_test.go
index 7264ee93..6b8ba64c 100644
--- a/envelope_test.go
+++ b/envelope_test.go
@@ -341,7 +341,7 @@ func TestEnvelopeReplicate(t *testing.T) {
 		require.NoError(t, err)
 
 		doc := env.Extract().(*bill.Invoice)
-		assert.Equal(t, "SAMPLE-001", doc.Code, "should not update in place")
+		assert.Equal(t, "SAMPLE-001", doc.Code.String(), "should not update in place")
 
 		e2, err := env.Replicate()
 		require.NoError(t, err)
diff --git a/internal/cli/bulk_test.go b/internal/cli/bulk_test.go
index c787605d..e46a1318 100644
--- a/internal/cli/bulk_test.go
+++ b/internal/cli/bulk_test.go
@@ -648,7 +648,7 @@ func TestBulk(t *testing.T) { //nolint:gocyclo
 				// Following raw message is copied and pasted! (sorry!)
 				Payload: json.RawMessage(`{
 					"list": [
-						"https://gobl.org/draft-0/bill/correction-options", "https://gobl.org/draft-0/bill/invoice", "https://gobl.org/draft-0/cal/date", "https://gobl.org/draft-0/cal/date-time", "https://gobl.org/draft-0/cal/period", "https://gobl.org/draft-0/cbc/code", "https://gobl.org/draft-0/cbc/code-map", "https://gobl.org/draft-0/cbc/key", "https://gobl.org/draft-0/cbc/key-definition", "https://gobl.org/draft-0/cbc/meta", "https://gobl.org/draft-0/cbc/note", "https://gobl.org/draft-0/cbc/value-definition", "https://gobl.org/draft-0/currency/amount", "https://gobl.org/draft-0/currency/code", "https://gobl.org/draft-0/currency/exchange-rate", "https://gobl.org/draft-0/dsig/digest", "https://gobl.org/draft-0/dsig/signature", "https://gobl.org/draft-0/envelope", "https://gobl.org/draft-0/head/header", "https://gobl.org/draft-0/head/link", "https://gobl.org/draft-0/head/stamp", "https://gobl.org/draft-0/i18n/string", "https://gobl.org/draft-0/l10n/code", "https://gobl.org/draft-0/l10n/iso-country-code", "https://gobl.org/draft-0/l10n/tax-country-code", "https://gobl.org/draft-0/note/message", "https://gobl.org/draft-0/num/amount", "https://gobl.org/draft-0/num/percentage", "https://gobl.org/draft-0/org/address", "https://gobl.org/draft-0/org/coordinates", "https://gobl.org/draft-0/org/email", "https://gobl.org/draft-0/org/identity", "https://gobl.org/draft-0/org/image", "https://gobl.org/draft-0/org/inbox", "https://gobl.org/draft-0/org/item", "https://gobl.org/draft-0/org/name", "https://gobl.org/draft-0/org/party", "https://gobl.org/draft-0/org/person", "https://gobl.org/draft-0/org/registration", "https://gobl.org/draft-0/org/telephone", "https://gobl.org/draft-0/org/unit", "https://gobl.org/draft-0/org/website", "https://gobl.org/draft-0/pay/advance", "https://gobl.org/draft-0/pay/instructions", "https://gobl.org/draft-0/pay/terms", "https://gobl.org/draft-0/regimes/mx/food-vouchers", "https://gobl.org/draft-0/regimes/mx/fuel-account-balance", "https://gobl.org/draft-0/schema/object", "https://gobl.org/draft-0/tax/addon-def", "https://gobl.org/draft-0/tax/extensions", "https://gobl.org/draft-0/tax/identity", "https://gobl.org/draft-0/tax/regime-def", "https://gobl.org/draft-0/tax/set", "https://gobl.org/draft-0/tax/total"
+						"https://gobl.org/draft-0/bill/correction-options", "https://gobl.org/draft-0/bill/invoice", "https://gobl.org/draft-0/cal/date", "https://gobl.org/draft-0/cal/date-time", "https://gobl.org/draft-0/cal/period", "https://gobl.org/draft-0/cbc/code", "https://gobl.org/draft-0/cbc/code-map", "https://gobl.org/draft-0/cbc/key", "https://gobl.org/draft-0/cbc/key-definition", "https://gobl.org/draft-0/cbc/meta", "https://gobl.org/draft-0/cbc/note", "https://gobl.org/draft-0/cbc/value-definition", "https://gobl.org/draft-0/currency/amount", "https://gobl.org/draft-0/currency/code", "https://gobl.org/draft-0/currency/exchange-rate", "https://gobl.org/draft-0/dsig/digest", "https://gobl.org/draft-0/dsig/signature", "https://gobl.org/draft-0/envelope", "https://gobl.org/draft-0/head/header", "https://gobl.org/draft-0/head/link", "https://gobl.org/draft-0/head/stamp", "https://gobl.org/draft-0/i18n/string", "https://gobl.org/draft-0/l10n/code", "https://gobl.org/draft-0/l10n/iso-country-code", "https://gobl.org/draft-0/l10n/tax-country-code", "https://gobl.org/draft-0/note/message", "https://gobl.org/draft-0/num/amount", "https://gobl.org/draft-0/num/percentage", "https://gobl.org/draft-0/org/address", "https://gobl.org/draft-0/org/coordinates", "https://gobl.org/draft-0/org/document-ref", "https://gobl.org/draft-0/org/email", "https://gobl.org/draft-0/org/identity", "https://gobl.org/draft-0/org/image", "https://gobl.org/draft-0/org/inbox", "https://gobl.org/draft-0/org/item", "https://gobl.org/draft-0/org/name", "https://gobl.org/draft-0/org/party", "https://gobl.org/draft-0/org/person", "https://gobl.org/draft-0/org/registration", "https://gobl.org/draft-0/org/telephone", "https://gobl.org/draft-0/org/unit", "https://gobl.org/draft-0/org/website", "https://gobl.org/draft-0/pay/advance", "https://gobl.org/draft-0/pay/instructions", "https://gobl.org/draft-0/pay/terms", "https://gobl.org/draft-0/regimes/mx/food-vouchers", "https://gobl.org/draft-0/regimes/mx/fuel-account-balance", "https://gobl.org/draft-0/schema/object", "https://gobl.org/draft-0/tax/addon-def", "https://gobl.org/draft-0/tax/extensions", "https://gobl.org/draft-0/tax/identity", "https://gobl.org/draft-0/tax/regime-def", "https://gobl.org/draft-0/tax/set", "https://gobl.org/draft-0/tax/total"
 					]
 				}`),
 				IsFinal: false,
diff --git a/org/document_ref.go b/org/document_ref.go
new file mode 100644
index 00000000..48661f1f
--- /dev/null
+++ b/org/document_ref.go
@@ -0,0 +1,92 @@
+package org
+
+import (
+	"context"
+
+	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/cbc"
+	"github.com/invopop/gobl/head"
+	"github.com/invopop/gobl/tax"
+	"github.com/invopop/gobl/uuid"
+	"github.com/invopop/jsonschema"
+	"github.com/invopop/validation"
+	"github.com/invopop/validation/is"
+)
+
+// DocumentRef is used to describe an existing document or a specific part of it's contents.
+type DocumentRef struct {
+	uuid.Identify
+	// Type of the document referenced.
+	Type cbc.Key `json:"type,omitempty" jsonschema:"title=Type"`
+	// IssueDate reflects the date the document was issued.
+	IssueDate *cal.Date `json:"issue_date,omitempty" jsonschema:"title=Issue Date"`
+	// Series the referenced document belongs to.
+	Series cbc.Code `json:"series,omitempty" jsonschema:"title=Series"`
+	// Source document's code or other identifier.
+	Code cbc.Code `json:"code" jsonschema:"title=Code"`
+	// Line index number inside the document, if relevant.
+	Line int `json:"line,omitempty" jsonschema:"title=Line"`
+	// List of additional codes, IDs, or SKUs which can be used to identify the document or its contents, agreed upon by the supplier and customer.
+	Identities []*Identity `json:"identities,omitempty" jsonschema:"title=Identities"`
+	// Tax period in which the referred document had an effect required by some tax regimes and formats.
+	Period *cal.Period `json:"period,omitempty" jsonschema:"title=Period"`
+	// Human readable description on why this reference is here or needs to be used.
+	Reason string `json:"reason,omitempty" jsonschema:"title=Reason"`
+	// Additional details about the document.
+	Description string `json:"description,omitempty" jsonschema:"title=Description"`
+	// Seals of approval from other organisations that may need to be listed.
+	Stamps []*head.Stamp `json:"stamps,omitempty" jsonschema:"title=Stamps"`
+	// Link to the source document.
+	URL string `json:"url,omitempty" jsonschema:"title=URL,format=uri"`
+	// Extensions for additional codes that may be required.
+	Ext tax.Extensions `json:"ext,omitempty" jsonschemaL:"title=Extensions"`
+	// Meta contains additional information about the document.
+	Meta cbc.Meta `json:"meta,omitempty" jsonschema:"title=Meta"`
+}
+
+// Normalize attempts to clean and normalize the DocumentRef.
+func (dr *DocumentRef) Normalize(normalizers tax.Normalizers) {
+	if dr == nil {
+		return
+	}
+	dr.Ext = tax.CleanExtensions(dr.Ext)
+	dr.Series = cbc.NormalizeCode(dr.Series)
+	dr.Code = cbc.NormalizeCode(dr.Code)
+	normalizers.Each(dr)
+	tax.Normalize(normalizers, dr.Identities)
+}
+
+// Validate ensures the Document looks correct.
+func (dr *DocumentRef) Validate() error {
+	return dr.ValidateWithContext(context.Background())
+}
+
+// ValidateWithContext ensures the Document looks correct within the provided context.
+func (dr *DocumentRef) ValidateWithContext(ctx context.Context) error {
+	return tax.ValidateStructWithContext(ctx, dr,
+		validation.Field(&dr.UUID),
+		validation.Field(&dr.Type),
+		validation.Field(&dr.IssueDate, cal.DateNotZero()),
+		validation.Field(&dr.Series),
+		validation.Field(&dr.Code,
+			validation.Match(cbc.CodePatternRegexp),
+			validation.Required,
+		),
+		validation.Field(&dr.URL, is.URL),
+		validation.Field(&dr.Stamps),
+		validation.Field(&dr.Period),
+		validation.Field(&dr.Ext),
+		validation.Field(&dr.Meta),
+	)
+}
+
+// JSONSchemaExtend extends the schema with additional property details
+func (DocumentRef) JSONSchemaExtend(schema *jsonschema.Schema) {
+	props := schema.Properties
+	if prop, ok := props.Get("series"); ok {
+		prop.Pattern = cbc.CodePattern
+	}
+	if prop, ok := props.Get("code"); ok {
+		prop.Pattern = cbc.CodePattern
+	}
+}
diff --git a/org/document_ref_test.go b/org/document_ref_test.go
new file mode 100644
index 00000000..52473583
--- /dev/null
+++ b/org/document_ref_test.go
@@ -0,0 +1,31 @@
+package org_test
+
+import (
+	"testing"
+
+	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/org"
+	"github.com/invopop/gobl/tax"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDocumentRefValidation(t *testing.T) {
+	dr := new(org.DocumentRef)
+	dr.Code = "FOO"
+	dr.IssueDate = cal.NewDate(2022, 11, 6)
+
+	err := dr.Validate()
+	assert.NoError(t, err)
+}
+
+func TestDocumentNormalize(t *testing.T) {
+	dr := &org.DocumentRef{
+		Code: " Foo ",
+		Ext: tax.Extensions{
+			"fooo": "",
+		},
+	}
+	dr.Normalize(nil)
+	assert.Equal(t, "FOO", dr.Code.String())
+	assert.Empty(t, dr.Ext)
+}
diff --git a/org/org.go b/org/org.go
index 21d737c8..9db88b8d 100644
--- a/org/org.go
+++ b/org/org.go
@@ -7,6 +7,7 @@ func init() {
 	schema.Register(schema.GOBL.Add("org"),
 		Address{},
 		Coordinates{},
+		DocumentRef{},
 		Email{},
 		Identity{},
 		Image{},
diff --git a/regimes/co/invoices.go b/regimes/co/invoices.go
index 57c66046..9143b5ad 100644
--- a/regimes/co/invoices.go
+++ b/regimes/co/invoices.go
@@ -138,7 +138,7 @@ func municipalityCodeRequired(tID *tax.Identity) bool {
 }
 
 func (v *invoiceValidator) preceding(value interface{}) error {
-	obj, ok := value.(*bill.Preceding)
+	obj, ok := value.(*org.DocumentRef)
 	if !ok || obj == nil {
 		return nil
 	}
diff --git a/regimes/co/invoices_test.go b/regimes/co/invoices_test.go
index d50fb033..8441404a 100644
--- a/regimes/co/invoices_test.go
+++ b/regimes/co/invoices_test.go
@@ -68,7 +68,7 @@ func creditNote() *bill.Invoice {
 		Code:      "TEST",
 		Type:      bill.InvoiceTypeCreditNote,
 		IssueDate: cal.MakeDate(2022, 12, 29),
-		Preceding: []*bill.Preceding{
+		Preceding: []*org.DocumentRef{
 			{
 				Code:      "TEST",
 				IssueDate: cal.NewDate(2022, 12, 27),
diff --git a/regimes/gr/README.md b/regimes/gr/README.md
index 19ecd376..35ba2bde 100644
--- a/regimes/gr/README.md
+++ b/regimes/gr/README.md
@@ -65,7 +65,7 @@ And this is how you'll get the same result by using the GOBL type and tags:
 
 Greece has three VAT rates: standard, reduced and super-reduced. Each of these rates are reduced by a 30% on the islands of Leros, Lesbos, Kos, Samos and Chios. The tax authority identifies each rate with a specific VAT category.
 
-In GOBL, the IAPR VAT category code must be set using the `gr-mydata-vat-cat` extension of a line's tax to one of the codes:
+In GOBL, the IAPR VAT category code must be set using the `gr-mydata-vat-rate` extension of a line's tax to one of the codes:
 
 | Code | Description                 | GOBL Rate              |
 | ---- | --------------------------- | ---------------------- |
@@ -79,7 +79,7 @@ In GOBL, the IAPR VAT category code must be set using the `gr-mydata-vat-cat` ex
 | `8`  | Records without VAT         |                        |
 
 
-Please, note that GOBL will automatically set the proper `gr-mydata-vat-cat` code and tax percent automatically when the line tax uses any of the GOBL rates specified in the table above. For example:
+Please, note that GOBL will automatically set the proper `gr-mydata-vat-rate` code and tax percent automatically when the line tax uses any of the GOBL rates specified in the table above. For example:
 
 ```js
 {
@@ -200,7 +200,7 @@ For example:
 
 Invoices reported to the Greek tax authority via myDATA can optionally include information about the income classification of each invoice item.
 
-In a GOBL invoice, the `gr-mydata-income-cat` and `gr-mydata-income-type` extensions can be set at line tax level to any of the values expected by the IAPR:
+In a GOBL invoice, the `gr-mydata-income-cat` and `gr-mydata-income-type` extensions can be set at item level to any of the values expected by the IAPR:
 
 #### Income Category
 
@@ -266,20 +266,12 @@ For example:
     "quantity": "20",
     "item": {
       "name": "Υπηρεσίες Ανάπτυξης",
-      "price": "90.00"
-    },
-    // ...
-    "taxes": [
-      {
-        "cat": "VAT",
-        "rate": "standard",
-        "ext": {
-          "gr-mydata-income-cat": "category1_1",
-          "gr-mydata-income-type": "E3_106",
-          // ...
-        }
+      "price": "90.00",
+      "ext": {
+        "gr-mydata-income-cat": "category1_1",
+        "gr-mydata-income-type": "E3_561_001",
       }
-    ]
+    }
   }
 ]
 ```
diff --git a/regimes/mx/sat/corrections.go b/regimes/mx/corrections.go
similarity index 58%
rename from regimes/mx/sat/corrections.go
rename to regimes/mx/corrections.go
index 999eef45..8033b251 100644
--- a/regimes/mx/sat/corrections.go
+++ b/regimes/mx/corrections.go
@@ -1,4 +1,4 @@
-package sat
+package mx
 
 import (
 	"github.com/invopop/gobl/bill"
@@ -6,11 +6,6 @@ import (
 	"github.com/invopop/gobl/tax"
 )
 
-// CorrectionDefinitions provides the array of correction definitions that apply to SAT
-func CorrectionDefinitions() []*tax.CorrectionDefinition {
-	return correctionDefinitions
-}
-
 var correctionDefinitions = []*tax.CorrectionDefinition{
 	{
 		Schema: bill.ShortSchemaInvoice,
@@ -18,7 +13,7 @@ var correctionDefinitions = []*tax.CorrectionDefinition{
 			bill.InvoiceTypeCreditNote,
 		},
 		Stamps: []cbc.Key{
-			StampUUID,
+			StampSATUUID,
 		},
 	},
 }
diff --git a/regimes/mx/invoice.go b/regimes/mx/invoice.go
new file mode 100644
index 00000000..c7a92bdb
--- /dev/null
+++ b/regimes/mx/invoice.go
@@ -0,0 +1,40 @@
+package mx
+
+import (
+	"github.com/invopop/gobl/bill"
+	"github.com/invopop/gobl/cbc"
+	"github.com/invopop/gobl/tax"
+)
+
+const (
+	// constants copied from CFDI
+	extKeyIssuePlace cbc.Key = "mx-cfdi-issue-place"
+	extKeyPostCode   cbc.Key = "mx-cfdi-post-code"
+)
+
+func normalizeInvoice(inv *bill.Invoice) {
+	// 2024-04-26: copy suppliers post code to invoice, if not already
+	// set.
+	normalizeParty(inv.Supplier) // first do party
+	ext := make(tax.Extensions)
+	if inv.Tax != nil {
+		ext = inv.Tax.Ext
+	}
+	if ext.Has(extKeyIssuePlace) {
+		return
+	}
+	if inv.Supplier != nil && inv.Supplier.Ext.Has(extKeyPostCode) {
+		ext[extKeyIssuePlace] = inv.Supplier.Ext[extKeyPostCode]
+	} else if len(inv.Supplier.Addresses) > 0 {
+		addr := inv.Supplier.Addresses[0]
+		if addr.Code != "" {
+			ext[extKeyIssuePlace] = tax.ExtValue(addr.Code)
+		}
+	}
+	if len(ext) > 0 {
+		if inv.Tax == nil {
+			inv.Tax = new(bill.Tax)
+		}
+		inv.Tax.Ext = ext
+	}
+}
diff --git a/regimes/mx/invoice_test.go b/regimes/mx/invoice_test.go
new file mode 100644
index 00000000..c0223988
--- /dev/null
+++ b/regimes/mx/invoice_test.go
@@ -0,0 +1,120 @@
+package mx_test
+
+import (
+	"testing"
+
+	"github.com/invopop/gobl/addons/mx/cfdi"
+	"github.com/invopop/gobl/bill"
+	"github.com/invopop/gobl/cal"
+	"github.com/invopop/gobl/num"
+	"github.com/invopop/gobl/org"
+	"github.com/invopop/gobl/tax"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNormalizeInvoice(t *testing.T) {
+	t.Run("no tax", func(t *testing.T) {
+		inv := baseInvoice()
+		require.NoError(t, inv.Calculate())
+		require.NoError(t, inv.Validate())
+		require.NotNil(t, inv.Tax)
+		assert.Equal(t, tax.ExtValue("21000"), inv.Tax.Ext[cfdi.ExtKeyIssuePlace])
+	})
+	t.Run("with supplier address code", func(t *testing.T) {
+		inv := baseInvoice()
+		delete(inv.Supplier.Ext, cfdi.ExtKeyPostCode)
+		inv.Supplier.Addresses = append(inv.Supplier.Addresses,
+			&org.Address{
+				Locality: "Mexico",
+				Code:     "21000",
+			},
+		)
+		require.NoError(t, inv.Calculate())
+		require.NoError(t, inv.Validate())
+		require.NotNil(t, inv.Tax)
+		assert.Equal(t, tax.ExtValue("21000"), inv.Tax.Ext[cfdi.ExtKeyIssuePlace])
+	})
+	t.Run("migrate supplier issue place", func(t *testing.T) {
+		inv := baseInvoice()
+		inv.Tax = nil
+		inv.Supplier.Ext = tax.Extensions{
+			cfdi.ExtKeyPostCode: "12345",
+		}
+		require.NoError(t, inv.Calculate())
+		require.NoError(t, inv.Validate())
+		require.NotNil(t, inv.Tax)
+		assert.Equal(t, tax.ExtValue("12345"), inv.Tax.Ext[cfdi.ExtKeyIssuePlace])
+	})
+	t.Run("migrate supplier issue place", func(t *testing.T) {
+		inv := baseInvoice()
+		inv.Tax = nil
+		inv.Supplier.Ext = nil
+		inv.Supplier.Addresses = append(inv.Supplier.Addresses,
+			&org.Address{
+				Locality: "Mexico",
+				Code:     "12345",
+			},
+		)
+		require.NoError(t, inv.Calculate())
+		require.NoError(t, inv.Validate())
+		require.NotNil(t, inv.Tax)
+		assert.Equal(t, tax.ExtValue("12345"), inv.Tax.Ext[cfdi.ExtKeyIssuePlace])
+	})
+}
+
+func baseInvoice() *bill.Invoice {
+	return &bill.Invoice{
+		Regime:    tax.WithRegime("MX"),
+		Code:      "123",
+		Currency:  "MXN",
+		IssueDate: cal.MakeDate(2023, 1, 1),
+		Tax: &bill.Tax{
+			Ext: tax.Extensions{
+				cfdi.ExtKeyIssuePlace: "21000",
+			},
+		},
+		Supplier: &org.Party{
+			Name: "Test Supplier",
+			Ext: tax.Extensions{
+				cfdi.ExtKeyPostCode:     "21000",
+				cfdi.ExtKeyFiscalRegime: "601",
+			},
+			TaxID: &tax.Identity{
+				Country: "MX",
+				Code:    "AAA010101AAA",
+			},
+		},
+		Customer: &org.Party{
+			Name: "Test Customer",
+			Ext: tax.Extensions{
+				cfdi.ExtKeyPostCode:     "65000",
+				cfdi.ExtKeyFiscalRegime: "608",
+				cfdi.ExtKeyUse:          "G01",
+			},
+			TaxID: &tax.Identity{
+				Country: "MX",
+				Code:    "ZZZ010101ZZZ",
+			},
+		},
+		Lines: []*bill.Line{
+			{
+				Quantity: num.MakeAmount(1, 0),
+				Item: &org.Item{
+					Name:  "bogus",
+					Price: num.MakeAmount(10000, 2),
+					Unit:  org.UnitPackage,
+					Ext: tax.Extensions{
+						cfdi.ExtKeyProdServ: "01010101",
+					},
+				},
+				Taxes: tax.Set{
+					{
+						Category: "VAT",
+						Rate:     "standard",
+					},
+				},
+			},
+		},
+	}
+}
diff --git a/regimes/mx/mx.go b/regimes/mx/mx.go
index 5ac11b6d..8074ac23 100644
--- a/regimes/mx/mx.go
+++ b/regimes/mx/mx.go
@@ -2,19 +2,36 @@
 package mx
 
 import (
+	"github.com/invopop/gobl/bill"
+	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/currency"
 	"github.com/invopop/gobl/i18n"
+	"github.com/invopop/gobl/org"
 	"github.com/invopop/gobl/regimes/common"
-	"github.com/invopop/gobl/regimes/mx/sat"
 	"github.com/invopop/gobl/tax"
 )
 
 func init() {
 	tax.RegisterRegimeDef(New())
+}
 
-	// MX GOBL Schema Complements for CFDI
+// Official SAT codes to include in stamps.
+const (
+	StampSATSignature   cbc.Key = "sat-sig"          // Signature - Sello Digital del SAT (optional)
+	StampSATSerial      cbc.Key = "sat-serial"       // Cert Serial - Número de Certificado SAT
+	StampSATTimestamp   cbc.Key = "sat-timestamp"    // Timestamp - Fecha y hora de certificación del SAT
+	StampSATUUID        cbc.Key = "sat-uuid"         // Folio Fiscal
+	StampSATURL         cbc.Key = "sat-url"          // URL QR Code
+	StampSATProviderRFC cbc.Key = "sat-provider-rfc" // Provider RFC - RFC del Proveedor de Certificación
+	StampSATChain       cbc.Key = "sat-chain"        // Cadena original del complemento de certificación digital del SAT
+)
 
-}
+// Custom keys used typically in meta or codes information.
+const (
+	KeyFormaPago    cbc.Key = "sat-forma-pago"    // for mapping to c_FormaPago’s codes
+	KeyTipoRelacion cbc.Key = "sat-tipo-relacion" // for mapping to c_TipoRelacion’s codes
+	KeyImpuesto     cbc.Key = "sat-impuesto"      // for mapping to c_Impuesto’s codes
+)
 
 // New provides the tax region definition
 func New() *tax.RegimeDef {
@@ -31,24 +48,28 @@ func New() *tax.RegimeDef {
 		Tags: []*tax.TagSet{
 			common.InvoiceTags(),
 		},
-		Categories:  sat.TaxCategories(),
-		Corrections: sat.CorrectionDefinitions(),
+		Categories:  taxCategories,
+		Corrections: correctionDefinitions,
 	}
 }
 
-// Validate validates a document against the tax regime.
-func Validate(doc any) error {
+// Normalize performs regime specific calculations.
+func Normalize(doc any) {
 	switch obj := doc.(type) {
+	case *bill.Invoice:
+		normalizeInvoice(obj)
 	case *tax.Identity:
-		return sat.ValidateTaxIdentity(obj)
+		tax.NormalizeIdentity(obj)
+	case *org.Party:
+		normalizeParty(obj)
 	}
-	return nil
 }
 
-// Normalize performs regime specific calculations.
-func Normalize(doc any) {
+// Validate validates a document against the tax regime.
+func Validate(doc any) error {
 	switch obj := doc.(type) {
 	case *tax.Identity:
-		tax.NormalizeIdentity(obj)
+		return ValidateTaxIdentity(obj)
 	}
+	return nil
 }
diff --git a/regimes/mx/party.go b/regimes/mx/party.go
new file mode 100644
index 00000000..b10b397c
--- /dev/null
+++ b/regimes/mx/party.go
@@ -0,0 +1,20 @@
+package mx
+
+import (
+	"github.com/invopop/gobl/org"
+	"github.com/invopop/gobl/tax"
+)
+
+func normalizeParty(p *org.Party) {
+	if p == nil {
+		return
+	}
+	// 2024-03-14: Migrate Tax ID Zone to extensions "mx-cfdi-post-code"
+	if p.TaxID != nil && p.TaxID.Zone != "" { //nolint:staticcheck
+		if p.Ext == nil {
+			p.Ext = make(tax.Extensions)
+		}
+		p.Ext[extKeyPostCode] = tax.ExtValue(p.TaxID.Zone) //nolint:staticcheck
+		p.TaxID.Zone = ""                                  //nolint:staticcheck
+	}
+}
diff --git a/regimes/mx/party_test.go b/regimes/mx/party_test.go
new file mode 100644
index 00000000..49ffa8df
--- /dev/null
+++ b/regimes/mx/party_test.go
@@ -0,0 +1,27 @@
+package mx_test
+
+import (
+	"testing"
+
+	"github.com/invopop/gobl/addons/mx/cfdi"
+	"github.com/invopop/gobl/org"
+	"github.com/invopop/gobl/tax"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMigratePartyIdentities(t *testing.T) {
+	customer := &org.Party{
+		Name: "Test Customer",
+		TaxID: &tax.Identity{
+			Country: "MX",
+			Code:    "ZZZ010101ZZZ",
+			Zone:    "65000",
+		},
+	}
+
+	mx := tax.RegimeDefFor("MX")
+	mx.Normalizer(customer)
+
+	assert.Equal(t, "65000", customer.Ext[cfdi.ExtKeyPostCode].String())
+	assert.Empty(t, customer.TaxID.Zone) //nolint:staticcheck
+}
diff --git a/regimes/mx/sat/sat.go b/regimes/mx/sat/sat.go
deleted file mode 100644
index 568d18d2..00000000
--- a/regimes/mx/sat/sat.go
+++ /dev/null
@@ -1,23 +0,0 @@
-// Package sat provides specifications from the Mexican SAT
-// (Servicio de Administración Tributaria) tax authority.
-package sat
-
-import "github.com/invopop/gobl/cbc"
-
-// Official SAT codes to include in stamps.
-const (
-	StampSignature   cbc.Key = "sat-sig"          // Signature - Sello Digital del SAT (optional)
-	StampSerial      cbc.Key = "sat-serial"       // Cert Serial - Número de Certificado SAT
-	StampTimestamp   cbc.Key = "sat-timestamp"    // Timestamp - Fecha y hora de certificación del SAT
-	StampUUID        cbc.Key = "sat-uuid"         // Folio Fiscal
-	StampURL         cbc.Key = "sat-url"          // URL QR Code
-	StampProviderRFC cbc.Key = "sat-provider-rfc" // Provider RFC - RFC del Proveedor de Certificación
-	StampChain       cbc.Key = "sat-chain"        // Cadena original del complemento de certificación digital del SAT
-)
-
-// Custom keys used typically in meta or codes information.
-const (
-	KeyFormaPago    cbc.Key = "sat-forma-pago"    // for mapping to c_FormaPago’s codes
-	KeyTipoRelacion cbc.Key = "sat-tipo-relacion" // for mapping to c_TipoRelacion’s codes
-	KeyImpuesto     cbc.Key = "sat-impuesto"      // for mapping to c_Impuesto’s codes
-)
diff --git a/regimes/mx/sat/tax_categories.go b/regimes/mx/tax_categories.go
similarity index 95%
rename from regimes/mx/sat/tax_categories.go
rename to regimes/mx/tax_categories.go
index 6514c05a..e99ce943 100644
--- a/regimes/mx/sat/tax_categories.go
+++ b/regimes/mx/tax_categories.go
@@ -1,4 +1,4 @@
-package sat
+package mx
 
 import (
 	"github.com/invopop/gobl/cbc"
@@ -20,11 +20,6 @@ const (
 	TaxRateExempt cbc.Key = "exempt"
 )
 
-// TaxCategories returns the list of tax categories used in Mexico.
-func TaxCategories() []*tax.CategoryDef {
-	return taxCategories
-}
-
 var taxCategories = []*tax.CategoryDef{
 	//
 	// IVA
diff --git a/regimes/mx/sat/tax_identity.go b/regimes/mx/tax_identity.go
similarity index 99%
rename from regimes/mx/sat/tax_identity.go
rename to regimes/mx/tax_identity.go
index c601c36e..fe9e794a 100644
--- a/regimes/mx/sat/tax_identity.go
+++ b/regimes/mx/tax_identity.go
@@ -1,4 +1,4 @@
-package sat
+package mx
 
 import (
 	"regexp"
diff --git a/regimes/mx/sat/tax_identity_test.go b/regimes/mx/tax_identity_test.go
similarity index 86%
rename from regimes/mx/sat/tax_identity_test.go
rename to regimes/mx/tax_identity_test.go
index e71868db..e43b14ba 100644
--- a/regimes/mx/sat/tax_identity_test.go
+++ b/regimes/mx/tax_identity_test.go
@@ -1,4 +1,4 @@
-package sat_test
+package mx_test
 
 import (
 	"testing"
@@ -6,7 +6,6 @@ import (
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/l10n"
 	"github.com/invopop/gobl/regimes/mx"
-	"github.com/invopop/gobl/regimes/mx/sat"
 	"github.com/invopop/gobl/tax"
 	"github.com/stretchr/testify/assert"
 )
@@ -44,7 +43,7 @@ func TestTaxIdentityValidation(t *testing.T) {
 		zone l10n.Code
 		err  string
 	}{
-		{name: "foreign code", code: sat.TaxIdentityCodeForeign, zone: "21000"},
+		{name: "foreign code", code: mx.TaxIdentityCodeForeign, zone: "21000"},
 		{name: "valid code 1", code: "MNOP8201019HJ"},
 		{name: "valid code 2", code: "UVWX610715JKL"},
 		{name: "valid code 3", code: "STU760612MN1"},
@@ -97,16 +96,16 @@ func TestTaxIdentityDetermineType(t *testing.T) {
 			Type: cbc.KeyEmpty,
 		},
 		{
-			Code: sat.TaxIdentityCodeForeign,
-			Type: sat.TaxIdentityTypePerson,
+			Code: mx.TaxIdentityCodeForeign,
+			Type: mx.TaxIdentityTypePerson,
 		},
 		{
 			Code: "MNOP8201019HJ",
-			Type: sat.TaxIdentityTypePerson,
+			Type: mx.TaxIdentityTypePerson,
 		},
 		{
 			Code: "ABC830720XYZ",
-			Type: sat.TaxIdentityTypeCompany,
+			Type: mx.TaxIdentityTypeCompany,
 		},
 		{
 			Code: "XXXX",
@@ -115,7 +114,7 @@ func TestTaxIdentityDetermineType(t *testing.T) {
 	}
 	for _, ts := range tests {
 		t.Run(string(ts.Code), func(t *testing.T) {
-			res := sat.DetermineTaxCodeType(ts.Code)
+			res := mx.DetermineTaxCodeType(ts.Code)
 			assert.Equal(t, ts.Type, res)
 		})
 	}
diff --git a/regimes/pl/invoices.go b/regimes/pl/invoices.go
index e2076494..1bf5d181 100644
--- a/regimes/pl/invoices.go
+++ b/regimes/pl/invoices.go
@@ -83,7 +83,7 @@ func (v *invoiceValidator) commercialCustomer(value interface{}) error {
 }
 
 func (v *invoiceValidator) preceding(value interface{}) error {
-	obj, ok := value.(*bill.Preceding)
+	obj, ok := value.(*org.DocumentRef)
 	if !ok || obj == nil {
 		return nil
 	}
diff --git a/regimes/pl/invoices_test.go b/regimes/pl/invoices_test.go
index 106e06f1..e1417a2d 100644
--- a/regimes/pl/invoices_test.go
+++ b/regimes/pl/invoices_test.go
@@ -20,7 +20,7 @@ func creditNote() *bill.Invoice {
 		Code:      "TEST",
 		Type:      bill.InvoiceTypeCreditNote,
 		IssueDate: cal.MakeDate(2022, 12, 29),
-		Preceding: []*bill.Preceding{
+		Preceding: []*org.DocumentRef{
 			{
 				Code:      "TEST",
 				IssueDate: cal.NewDate(2022, 12, 27),
diff --git a/tax/addons.go b/tax/addons.go
index f044b410..438700cf 100644
--- a/tax/addons.go
+++ b/tax/addons.go
@@ -63,8 +63,13 @@ func (as *Addons) SetAddons(addons ...cbc.Key) {
 	as.List = addons
 }
 
-// GetAddons provides a slice of Addon instances.
-func (as Addons) GetAddons() []*AddonDef {
+// GetAddons provides the list of addon keys in use.
+func (as *Addons) GetAddons() []cbc.Key {
+	return as.List
+}
+
+// GetAddonDefs provides a slice of Addon Definition instances.
+func (as Addons) GetAddonDefs() []*AddonDef {
 	list := make([]*AddonDef, 0, len(as.List))
 	for _, ak := range as.List {
 		if a := AddonForKey(ak); a != nil {
diff --git a/tax/addons_test.go b/tax/addons_test.go
index 15a1b5dd..792807df 100644
--- a/tax/addons_test.go
+++ b/tax/addons_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"testing"
 
+	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/tax"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -22,7 +23,9 @@ func TestEmbeddingAddons(t *testing.T) {
 	assert.NotNil(t, ts.Addons)
 	assert.Equal(t, "Test", ts.Name)
 
-	defs := ts.GetAddons()
+	assert.Equal(t, []cbc.Key{"mx-cfdi-v4"}, ts.GetAddons())
+
+	defs := ts.GetAddonDefs()
 	assert.Len(t, defs, 1)
 	assert.Equal(t, "mx-cfdi-v4", defs[0].Key.String())
 
diff --git a/version.go b/version.go
index 32948394..4aa6ae3d 100644
--- a/version.go
+++ b/version.go
@@ -8,7 +8,7 @@ import (
 type Version string
 
 // VERSION is the current version of the GOBL library.
-const VERSION Version = "v0.200.0-rc1"
+const VERSION Version = "v0.200.0-rc2"
 
 // Semver parses and returns semver
 func (v Version) Semver() *semver.Version {