diff --git a/pkg/models/expense_classification.go b/pkg/models/expense_classification.go
index 4f5fdeb..18c425e 100644
--- a/pkg/models/expense_classification.go
+++ b/pkg/models/expense_classification.go
@@ -22,6 +22,8 @@ type InvoicesExpensesClassificationDetails struct {
 	ExpensesClassificationDetailData []ExpensesClassificationType `xml:"ExpensesClassificationDetailData"`
 }
 
+// MarshalXML transforms an ExpensesClassificationType to expensesClassificationType and serializes it in order to
+// include the `ecls` namespace for every field.
 func (classification ExpensesClassificationType) MarshalXML(enc *xml.Encoder, start xml.StartElement) error {
 	type expensesClassificationType struct {
 		ClassificationType     string  `xml:"ecls:classificationType"`
diff --git a/pkg/models/income_classification.go b/pkg/models/income_classification.go
index eb73f01..6942684 100644
--- a/pkg/models/income_classification.go
+++ b/pkg/models/income_classification.go
@@ -22,6 +22,8 @@ type InvoicesIncomeClassificationDetails struct {
 	IncomeClassificationDetailData []IncomeClassificationType `xml:"incomeClassificationDetailData"`
 }
 
+// MarshalXML transforms an IncomeClassificationType to incomeClassificationType and serializes it in order to include
+// the `icls` namespace for every field.
 func (classification IncomeClassificationType) MarshalXML(enc *xml.Encoder, start xml.StartElement) error {
 	type incomeClassificationType struct {
 		ClassificationType     string  `xml:"icls:classificationType"`