diff --git a/commonAttributes.go b/commonAttributes.go
index 2f13977..3c6473b 100644
--- a/commonAttributes.go
+++ b/commonAttributes.go
@@ -8,6 +8,22 @@ type CommonAttributes struct {
 	UndefinedAttributes []*ExtensionAttribute `xml:",any"`
 }
 
+// NewCommonAttributes creates a new set of CommonAttributes. It returns a
+// *CommonAttributes.
+func NewCommonAttributes() *CommonAttributes {
+	return new(CommonAttributes)
+}
+
+// AddExtensionAttribute adds the ExtensionAttribute to the CommonAttributes.
+func (c *CommonAttributes) AddExtensionAttribute(e *ExtensionAttribute) {
+	if c.UndefinedAttributes == nil {
+		c.UndefinedAttributes = make([]*ExtensionAttribute, 1)
+		c.UndefinedAttributes[0] = e
+	} else {
+		c.UndefinedAttributes = append(c.UndefinedAttributes, e)
+	}
+}
+
 // Check checks the CommonAttributes for incompatibilities with RFC4287. It
 // returns an error.
 func (c *CommonAttributes) Check() error {
diff --git a/extensionAttribute.go b/extensionAttribute.go
index d6fccb4..8e38700 100644
--- a/extensionAttribute.go
+++ b/extensionAttribute.go
@@ -1,20 +1,24 @@
 package atom
 
 import (
-	"encoding/xml"
 	"errors"
+	"fmt"
 )
 
-// TODO: Is this really correct?
 type ExtensionAttribute struct {
-	Value   any `xml:",attr"`
-	XMLName xml.Name
+	Attr string `xml:",attr"`
+}
+
+// NewExtensionAttribute creates a new ExtensionAttribute. It returns a
+// *ExtensionAttribute.
+func NewExtensionAttribute(name, value string) *ExtensionAttribute {
+	return &ExtensionAttribute{Attr: fmt.Sprint(name, `="`, value, `"`)}
 }
 
 // Check checks the ExtensionAttribute for incompatibilities with RFC4287. It
 // returns an error.
 func (e *ExtensionAttribute) Check() error {
-	if e.Value == nil {
+	if e.Attr == "" {
 		return errors.New("value element of extension attribute empty")
 	}
 
diff --git a/extensionElement.go b/extensionElement.go
index 77574b3..1f6c1d0 100644
--- a/extensionElement.go
+++ b/extensionElement.go
@@ -5,7 +5,6 @@ import (
 	"errors"
 )
 
-// TODO: Is this really correct?
 type ExtensionElement struct {
 	Value   any `xml:",innerxml"`
 	XMLName xml.Name