diff --git a/README.md b/README.md
index 144cbf8..2bb7266 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,6 @@ Marknl Iodef Library
 ====================
 [![Build Status](https://travis-ci.org/marknl/iodef.svg?branch=master)](https://travis-ci.org/marknl/iodef)
 [![Latest Stable Version](https://poser.pugx.org/marknl/iodef/v/stable)](https://packagist.org/packages/marknl/iodef)
-[![Latest Unstable Version](https://poser.pugx.org/marknl/iodef/v/unstable)](https://packagist.org/packages/marknl/iodef)
 [![Total Downloads](https://poser.pugx.org/marknl/iodef/downloads)](https://packagist.org/packages/marknl/iodef)
 [![License](https://poser.pugx.org/marknl/iodef/license)](https://packagist.org/packages/marknl/iodef)
 
diff --git a/composer.json b/composer.json
index 79c1982..939a3cd 100644
--- a/composer.json
+++ b/composer.json
@@ -5,32 +5,35 @@
     "homepage": "http://e-rave.nl/iodef",
     "type": "library",
     "license": "GPL-2.0",
-    "extra": {
-        "branch-alias": {
-            "dev-master": "1.x-dev"
-        }
-    },
     "authors": [
-		{
-			"name": "Mark Stunnenberg",
-			"email": "mark@e-rave.nl",
-			"homepage": "http://e-rave.nl/",
-			"role": "Lead"
-		}
-	],
+        {
+            "name": "Mark Stunnenberg",
+            "email": "mark@e-rave.nl",
+            "homepage": "http://e-rave.nl/",
+            "role": "Lead"
+        }
+    ],
     "support": {
         "issues": "https://github.com/marknl/iodef/issues",
         "source": "https://github.com/marknl/iodef"
     },
     "require": {
         "php": ">=5.5.0",
-	"sabre/xml": "1.5.*",
-	"sabre/uri": "1.2.*",
+        "sabre/xml": "1.5.*",
+        "sabre/uri": "1.2.*",
         "vlucas/valitron": "1.3.*"
     },
     "autoload": {
         "psr-4": {
             "Marknl\\Iodef\\": "src/"
+        },
+        "psr-0": {
+            "src/": ""
+        }
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-master": "1.x-dev"
         }
     }
 }
diff --git a/phpunit.xml b/phpunit.xml
index 856dbdb..3ebe3c1 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,5 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit backupGlobals="false"
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.5/phpunit.xsd"
+         backupGlobals="false"
          backupStaticAttributes="false"
          bootstrap="tests/bootstrap.php"
          colors="true"
diff --git a/src/Elements/AlternativeID.php b/src/Elements/AlternativeID.php
index 09ff4cc..bc2a85f 100644
--- a/src/Elements/AlternativeID.php
+++ b/src/Elements/AlternativeID.php
@@ -13,7 +13,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'IncidentID' => 'REQUIRED_MULTI',
+            'IncidentID' => parent::REQUIRED_MULTI,
         ];
     }
 
diff --git a/src/Elements/Application.php b/src/Elements/Application.php
index fbc10ba..ac9e3a2 100644
--- a/src/Elements/Application.php
+++ b/src/Elements/Application.php
@@ -19,7 +19,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'URL' => 'OPTIONAL',
+            'URL' => parent::OPTIONAL,
         ];
     }
 
diff --git a/src/Elements/Assessment.php b/src/Elements/Assessment.php
index 81c44f0..43c661f 100644
--- a/src/Elements/Assessment.php
+++ b/src/Elements/Assessment.php
@@ -14,12 +14,12 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Impact'            => 'OPTIONAL_MULTI',
-            'TimeImpact'        => 'OPTIONAL_MULTI',
-            'MonetaryImpact'    => 'OPTIONAL_MULTI',
-            'Counter'           => 'OPTIONAL_MULTI',
-            'Confidence'        => 'OPTIONAL',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'Impact'            => parent::OPTIONAL_MULTI,
+            'TimeImpact'        => parent::OPTIONAL_MULTI,
+            'MonetaryImpact'    => parent::OPTIONAL_MULTI,
+            'Counter'           => parent::OPTIONAL_MULTI,
+            'Confidence'        => parent::OPTIONAL,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Contact.php b/src/Elements/Contact.php
index 896add9..bba312a 100644
--- a/src/Elements/Contact.php
+++ b/src/Elements/Contact.php
@@ -17,16 +17,16 @@ public function __construct()
         ];
 
         $this->elements = [
-            'ContactName'       => 'OPTIONAL',
-            'Description'       => 'OPTIONAL_MULTI',
-            'RegistryHandle'    => 'OPTIONAL_MULTI',
-            'PostalAddress'     => 'OPTIONAL',
-            'Email'             => 'OPTIONAL_MULTI',
-            'Telephone'         => 'OPTIONAL_MULTI',
-            'Fax'               => 'OPTIONAL',
-            'Timezone'          => 'OPTIONAL',
-            'Contact'           => 'OPTIONAL_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'ContactName'       => parent::OPTIONAL,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'RegistryHandle'    => parent::OPTIONAL_MULTI,
+            'PostalAddress'     => parent::OPTIONAL,
+            'Email'             => parent::OPTIONAL_MULTI,
+            'Telephone'         => parent::OPTIONAL_MULTI,
+            'Fax'               => parent::OPTIONAL,
+            'Timezone'          => parent::OPTIONAL,
+            'Contact'           => parent::OPTIONAL_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/EventData.php b/src/Elements/EventData.php
index 36d9e05..f5f26d5 100644
--- a/src/Elements/EventData.php
+++ b/src/Elements/EventData.php
@@ -13,17 +13,17 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Description'       => 'OPTIONAL_MULTI',
-            'DetectTime'        => 'OPTIONAL',
-            'StartTime'         => 'OPTIONAL',
-            'Contact'           => 'OPTIONAL_MULTI',
-            'Assessment'        => 'OPTIONAL',
-            'Method'            => 'OPTIONAL_MULTI',
-            'Flow'              => 'OPTIONAL_MULTI',
-            'Expectation'       => 'OPTIONAL_MULTI',
-            'Record'            => 'OPTIONAL',
-            'EventData'         => 'OPTIONAL_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'Description'       => parent::OPTIONAL_MULTI,
+            'DetectTime'        => parent::OPTIONAL,
+            'StartTime'         => parent::OPTIONAL,
+            'Contact'           => parent::OPTIONAL_MULTI,
+            'Assessment'        => parent::OPTIONAL,
+            'Method'            => parent::OPTIONAL_MULTI,
+            'Flow'              => parent::OPTIONAL_MULTI,
+            'Expectation'       => parent::OPTIONAL_MULTI,
+            'Record'            => parent::OPTIONAL,
+            'EventData'         => parent::OPTIONAL_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Expectation.php b/src/Elements/Expectation.php
index 2390921..9aa6dcf 100644
--- a/src/Elements/Expectation.php
+++ b/src/Elements/Expectation.php
@@ -16,10 +16,10 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Description'   => 'OPTIONAL_MULTI',
-            'StartTime'     => 'OPTIONAL',
-            'EndTime'       => 'OPTIONAL',
-            'Contact'       => 'OPTIONAL',
+            'Description'   => parent::OPTIONAL_MULTI,
+            'StartTime'     => parent::OPTIONAL,
+            'EndTime'       => parent::OPTIONAL,
+            'Contact'       => parent::OPTIONAL,
         ];
     }
 
diff --git a/src/Elements/Flow.php b/src/Elements/Flow.php
index cfb4d65..09a70dd 100644
--- a/src/Elements/Flow.php
+++ b/src/Elements/Flow.php
@@ -9,7 +9,7 @@ class Flow extends IodefElement
     public function __construct()
     {
         $this->elements = [
-            'System'    => 'REQUIRED_MULTI',
+            'System'    => parent::REQUIRED_MULTI,
         ];
     }
 }
diff --git a/src/Elements/History.php b/src/Elements/History.php
index b2b80af..8e58ea2 100644
--- a/src/Elements/History.php
+++ b/src/Elements/History.php
@@ -13,7 +13,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'HistoryItem' => 'REQUIRED_MULTI',
+            'HistoryItem' => parent::REQUIRED_MULTI,
         ];
     }
 
diff --git a/src/Elements/HistoryItem.php b/src/Elements/HistoryItem.php
index e74514d..723d96a 100644
--- a/src/Elements/HistoryItem.php
+++ b/src/Elements/HistoryItem.php
@@ -15,11 +15,11 @@ public function __construct()
         ];
 
         $this->elements = [
-            'DateTime'          => 'REQUIRED',
-            'IncidentId'        => 'OPTIONAL',
-            'Contact'           => 'OPTIONAL',
-            'Description'       => 'OPTIONAL_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'DateTime'          => parent::REQUIRED,
+            'IncidentId'        => parent::OPTIONAL,
+            'Contact'           => parent::OPTIONAL,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/IODEFDocument.php b/src/Elements/IODEFDocument.php
index 3394ea5..35f274d 100644
--- a/src/Elements/IODEFDocument.php
+++ b/src/Elements/IODEFDocument.php
@@ -21,7 +21,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Incident' => 'REQUIRED_MULTI',
+            'Incident' => parent::REQUIRED_MULTI,
         ];
     }
 
diff --git a/src/Elements/Incident.php b/src/Elements/Incident.php
index 514a49b..90de2fe 100644
--- a/src/Elements/Incident.php
+++ b/src/Elements/Incident.php
@@ -16,20 +16,20 @@ public function __construct()
         ];
 
         $this->elements = [
-            'IncidentID'        => 'REQUIRED',
-            'AlternativeID'     => 'OPTIONAL',
-            'RelatedActivity'   => 'OPTIONAL',
-            'DetectTime'        => 'OPTIONAL',
-            'StartTime'         => 'OPTIONAL',
-            'EndTime'           => 'OPTIONAL',
-            'ReportTime'        => 'REQUIRED',
-            'Description'       => 'OPTIONAL_MULTI',
-            'Assessment'        => 'REQUIRED_MULTI',
-            'Method'            => 'OPTIONAL_MULTI',
-            'Contact'           => 'REQUIRED_MULTI',
-            'EventData'         => 'OPTIONAL_MULTI',
-            'History'           => 'OPTIONAL',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'IncidentID'        => parent::REQUIRED,
+            'AlternativeID'     => parent::OPTIONAL,
+            'RelatedActivity'   => parent::OPTIONAL,
+            'DetectTime'        => parent::OPTIONAL,
+            'StartTime'         => parent::OPTIONAL,
+            'EndTime'           => parent::OPTIONAL,
+            'ReportTime'        => parent::REQUIRED,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'Assessment'        => parent::REQUIRED_MULTI,
+            'Method'            => parent::OPTIONAL_MULTI,
+            'Contact'           => parent::REQUIRED_MULTI,
+            'EventData'         => parent::OPTIONAL_MULTI,
+            'History'           => parent::OPTIONAL,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Method.php b/src/Elements/Method.php
index 25384f9..6fe022e 100644
--- a/src/Elements/Method.php
+++ b/src/Elements/Method.php
@@ -13,9 +13,9 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Reference'         => 'OPTIONAL_MULTI',
-            'Description'       => 'OPTIONAL_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'Reference'         => parent::OPTIONAL_MULTI,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Node.php b/src/Elements/Node.php
index 812c90d..4a70f9c 100644
--- a/src/Elements/Node.php
+++ b/src/Elements/Node.php
@@ -9,12 +9,12 @@ class Node extends IodefElement
     public function __construct()
     {
         $this->elements = [
-            'NodeName'  => 'OPTIONAL_MULTI',
-            'Address'   => 'OPTIONAL_MULTI',
-            'Location'  => 'OPTIONAL',
-            'DateTime'  => 'OPTIONAL',
-            'NodeRole'  => 'OPTIONAL_MULTI',
-            'Counter'   => 'OPTIONAL_MULTI',
+            'NodeName'  => parent::OPTIONAL_MULTI,
+            'Address'   => parent::OPTIONAL_MULTI,
+            'Location'  => parent::OPTIONAL,
+            'DateTime'  => parent::OPTIONAL,
+            'NodeRole'  => parent::OPTIONAL_MULTI,
+            'Counter'   => parent::OPTIONAL_MULTI,
         ];
     }
 }
diff --git a/src/Elements/OperatingSystem.php b/src/Elements/OperatingSystem.php
index b6ed0bb..83eeaa1 100644
--- a/src/Elements/OperatingSystem.php
+++ b/src/Elements/OperatingSystem.php
@@ -19,7 +19,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'URL' => 'OPTIONAL',
+            'URL' => parent::OPTIONAL,
         ];
     }
 
diff --git a/src/Elements/Record.php b/src/Elements/Record.php
index da9bf57..d1bc13b 100644
--- a/src/Elements/Record.php
+++ b/src/Elements/Record.php
@@ -13,7 +13,7 @@ public function __construct()
         ];
 
         $this->elements = [
-            'RecordData' => 'REQUIRED_MULTI',
+            'RecordData' => parent::REQUIRED_MULTI,
         ];
     }
 
diff --git a/src/Elements/RecordData.php b/src/Elements/RecordData.php
index f9b2533..9109ce5 100644
--- a/src/Elements/RecordData.php
+++ b/src/Elements/RecordData.php
@@ -13,12 +13,12 @@ public function __construct()
         ];
 
         $this->elements = [
-            'DateTime'          => 'OPTIONAL',
-            'Description'       => 'OPTIONAL_MULTI',
-            'Application'       => 'OPTIONAL',
-            'RecordPattern'     => 'OPTIONAL_MULTI',
-            'RecordItem'        => 'REQUIRED_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'DateTime'          => parent::OPTIONAL,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'Application'       => parent::OPTIONAL,
+            'RecordPattern'     => parent::OPTIONAL_MULTI,
+            'RecordItem'        => parent::REQUIRED_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Reference.php b/src/Elements/Reference.php
index 2d74502..52ab441 100644
--- a/src/Elements/Reference.php
+++ b/src/Elements/Reference.php
@@ -9,9 +9,9 @@ class Reference extends IodefElement
     public function __construct()
     {
         $this->elements = [
-            'ReferenceName' => 'REQUIRED',
-            'URL'           => 'OPTIONAL_MULTI',
-            'Description'   => 'OPTIONAL_MULTI',
+            'ReferenceName' => parent::REQUIRED,
+            'URL'           => parent::OPTIONAL_MULTI,
+            'Description'   => parent::OPTIONAL_MULTI,
         ];
     }
 }
diff --git a/src/Elements/RelatedActivity.php b/src/Elements/RelatedActivity.php
index c54728e..1f456b7 100644
--- a/src/Elements/RelatedActivity.php
+++ b/src/Elements/RelatedActivity.php
@@ -13,8 +13,8 @@ public function __construct()
         ];
 
         $this->elements = [
-            'IncidentID'    => 'OPTIONAL_MULTI',
-            'URL'           => 'OPTIONAL_MULTI',
+            'IncidentID'    => parent::OPTIONAL_MULTI,
+            'URL'           => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/Elements/Service.php b/src/Elements/Service.php
index 575492a..18a8e81 100644
--- a/src/Elements/Service.php
+++ b/src/Elements/Service.php
@@ -13,12 +13,12 @@ public function __construct()
         ];
 
         $this->elements = [
-            'Port'          => 'OPTIONAL',
-            'Portlist'      => 'OPTIONAL',
-            'ProtoCode'     => 'OPTIONAL',
-            'ProtoType'     => 'OPTIONAL',
-            'ProtoFlags'    => 'OPTIONAL',
-            'Application'   => 'OPTIONAL',
+            'Port'          => parent::OPTIONAL,
+            'Portlist'      => parent::OPTIONAL,
+            'ProtoCode'     => parent::OPTIONAL,
+            'ProtoType'     => parent::OPTIONAL,
+            'ProtoFlags'    => parent::OPTIONAL,
+            'Application'   => parent::OPTIONAL,
         ];
     }
 
diff --git a/src/Elements/System.php b/src/Elements/System.php
index f333840..033013a 100644
--- a/src/Elements/System.php
+++ b/src/Elements/System.php
@@ -16,12 +16,12 @@ public function __construct()
             'spoofed'       => 'unknown',
         ];
         $this->elements = [
-            'Node'              => 'REQUIRED',
-            'Service'           => 'OPTIONAL_MULTI',
-            'OperatingSystem'   => 'OPTIONAL_MULTI',
-            'Counter'           => 'OPTIONAL_MULTI',
-            'Description'       => 'OPTIONAL_MULTI',
-            'AdditionalData'    => 'OPTIONAL_MULTI',
+            'Node'              => parent::REQUIRED,
+            'Service'           => parent::OPTIONAL_MULTI,
+            'OperatingSystem'   => parent::OPTIONAL_MULTI,
+            'Counter'           => parent::OPTIONAL_MULTI,
+            'Description'       => parent::OPTIONAL_MULTI,
+            'AdditionalData'    => parent::OPTIONAL_MULTI,
         ];
     }
 
diff --git a/src/IodefElement.php b/src/IodefElement.php
index e1767fb..d39c147 100644
--- a/src/IodefElement.php
+++ b/src/IodefElement.php
@@ -11,14 +11,15 @@
  * IODEF Element Class.
  * Provides a blueprint for all IODEF Element Types.
  *
- * @copyright Copyright (C) 2015-2016 Marknl (www.e-rave.nl)
+ * @copyright Copyright (C) 2015-2017 Marknl (www.e-rave.nl)
  * @author Mark Stunnenberg <mark@e-rave.nl>
  * @license http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
  */
 abstract class IodefElement implements SabreElement
 {
     /**
-     * The IODEF namespace as described in rfc-5070
+     * The IODEF namespace as described in rfc-5070.
+     * For more info: https://www.ietf.org/rfc/rfc5070.txt
      * @var string
      */
     protected $ns = '{urn:ietf:params:xml:ns:iodef-1.0}';
@@ -38,9 +39,33 @@ abstract class IodefElement implements SabreElement
     protected $elements = [];
 
     /**
-     * Get the ShortName of the given IodefObject
-     * @param  iodefElement $class
-     * @return string
+     * Constant for required element
+     * @var integer
+     */
+    const REQUIRED           = 0b00;
+
+    /**
+     * Constant for required array element
+     * @var integer
+     */
+    const REQUIRED_MULTI     = 0b01;
+
+    /**
+     * Constant for optional element
+     * @var integer
+     */
+    const OPTIONAL           = 0b10;
+
+    /**
+     * Constant for optional array element
+     * @var integer
+     */
+    const OPTIONAL_MULTI     = 0b11;
+
+    /**
+     * Get the short name of the given IodefObject.
+     * @param  iodefElement $class An instance of IodefElement.
+     * @return string Class name
      */
     public function getShortName($class = null)
     {
@@ -55,8 +80,8 @@ public function getShortName($class = null)
 
     /**
      * Add an attribute.
-     * @param string $name
-     * @param string $value
+     * @param array $attributes Array contists of standard name/value pair.
+     * @return void
      */
     public function setAttributes(array $attributes)
     {
@@ -66,8 +91,8 @@ public function setAttributes(array $attributes)
     }
 
     /**
-     * Get the attributes
-     * @return array
+     * Get the attributes.
+     * @return array List of attributes.
      */
     public function getAttributes()
     {
@@ -76,7 +101,7 @@ public function getAttributes()
 
     /**
      * Set the value of the element
-     * @param  mixed $value
+     * @param  mixed $value Value to be set.
      * @return void
      */
     public function value($value)
@@ -92,20 +117,24 @@ public function value($value)
     public function addChild($child)
     {
         $class = $this->getShortName($child);
+
+        // Only add child if it's an known element.
         if (array_key_exists($class, $this->elements)) {
-            if (substr($this->elements[$class], -6) == '_MULTI') {
+            // If we can expect more, add it to an array.
+            //if (substr($this->elements[$class], -6) == '_MULTI') {
+            if (in_array($this->elements[$class], [self::REQUIRED_MULTI, self::OPTIONAL_MULTI])) {
                 $this->{$class}[] = $child;
             } else {
                 $this->{$class} = $child;
             }
         } else {
-            die($this->getShortName(get_called_class()) .": {$class} is not allowed as child a element.");
+            die($this->getShortName(get_called_class()) .": {$class} is not allowed as a child element.");
         }
     }
 
     /**
-     * [getChildren description]
-     * @return void
+     * Get all chilren of the current IodefElement.
+     * @return array List of child elements.
      */
     protected function getChildren()
     {
@@ -114,6 +143,7 @@ protected function getChildren()
         foreach ($this->elements as $element => $occurrence) {
             switch ($occurrence) {
                 case 'REQUIRED':
+                case self::REQUIRED:
                     if (property_exists($this, $element)) {
                         $retArray[] = [
                             'name'          => $this->ns.$element,
@@ -127,6 +157,7 @@ protected function getChildren()
                     }
                     break;
                 case 'OPTIONAL':
+                case self::OPTIONAL:
                     if (property_exists($this, $element)) {
                         $retArray[] = [
                             'name'          => $this->ns.$element,
@@ -136,6 +167,7 @@ protected function getChildren()
                     }
                     break;
                 case 'REQUIRED_MULTI':
+                case self::REQUIRED_MULTI:
                     if (property_exists($this, $element)) {
                         foreach ($this->$element as $child) {
                             $retArray[] = [
@@ -151,6 +183,7 @@ protected function getChildren()
                     }
                     break;
                 case 'OPTIONAL_MULTI':
+                case self::OPTIONAL_MULTI:
                     if (property_exists($this, $element)) {
                         foreach ($this->$element as $child) {
                             $retArray[] = [
@@ -174,7 +207,7 @@ protected function getChildren()
 
     /**
      * Convert XML Elements to IodefElement Objects
-     * @param  SabreReader $reader [description]
+     * @param  SabreReader $reader
      * @return IodefElement
      */
     public static function xmlDeserialize(SabreReader $reader)
@@ -190,8 +223,9 @@ public static function xmlDeserialize(SabreReader $reader)
                 // This should always and only by of type 'object'.
                 if (gettype($child['value']) == 'object') {
                     $className = $child['value']->getShortName();
-
-                    if (substr($IodefElement->elements[$className], -6) == '_MULTI') {
+                    // We can expect multiple entries here, so add it to an array.
+                    //if (substr($IodefElement->elements[$className], -6) == '_MULTI') {
+                    if (in_array($IodefElement->elements[$className], [self::REQUIRED_MULTI, self::OPTIONAL_MULTI])) {
                         $IodefElement->{$className}[] = $child['value'];
                     } else {
                         $IodefElement->{$className} = $child['value'];
@@ -225,7 +259,7 @@ public function xmlSerialize(SabreWriter $writer)
                 $writer->write($this->getChildren());
             }
         } else {
-            die($this->getShortName(). ": Validation failed, see details above.");
+            die("\nValidation on element <".$this->getShortName()."> failed, see details above.\n");
         }
     }
 
@@ -264,12 +298,12 @@ protected function validate()
 
                 // Validation failed to succeeed, show errors
                 if (!$validate_value->validate()) {
-                    echo 'The value failed to pass the validator:';
+                    echo "The 'value' failed to pass the validator:";
                     foreach ($validate_value->errors() as $message) {
                         if (is_array($message)) {
-                           $message = implode(',', $message);
+                            $message = implode(',', $message);
                         }
-                        echo ' '. $message;
+                        echo ' '. strtolower($message);
                     }
                     return false;
                 }
diff --git a/src/Reader.php b/src/Reader.php
index 05d8064..c7dc283 100644
--- a/src/Reader.php
+++ b/src/Reader.php
@@ -13,6 +13,10 @@
  */
 class Reader extends SabreReader
 {
+    /**
+     * Constructor
+     * @param string $xml XML formatted string
+     */
     public function __construct($xml)
     {
         $this->elementMap = [
diff --git a/src/Writer.php b/src/Writer.php
index ded0499..d0d16c7 100644
--- a/src/Writer.php
+++ b/src/Writer.php
@@ -19,6 +19,9 @@ class Writer extends SabreWriter
      */
     public $formatOutput = false;
 
+    /**
+     * Contructor
+     */
     public function __construct()
     {
         $this->openMemory();
@@ -31,8 +34,7 @@ public function __construct()
     }
 
     /**
-     * Overwrite the original method, so we can add some output
-     * formatting for the XML.
+     * Overwrite the original method, so we can add some output formatting for the XML.
      * @param  boolval $flush Flush memory after
      * @return string
      */
diff --git a/tests/WriterTest.php b/tests/WriterTest.php
index 4130749..af9030c 100644
--- a/tests/WriterTest.php
+++ b/tests/WriterTest.php
@@ -145,6 +145,12 @@ public function testWriter()
 
             $Incident->addChild($EventData);
 
+                $AdditionalData = new Marknl\Iodef\Elements\AdditionalData();
+                $AdditionalData->setAttributes(['dtype' => 'string', 'meaning' => 'IODEF Test']);
+                $AdditionalData->value('Some additional data');
+
+            $Incident->addChild($AdditionalData);
+
         $Document->addChild($Incident);
 
         $iodef = new Marknl\Iodef\Writer();
diff --git a/tests/iodef.xml b/tests/iodef.xml
index 8b88f62..e9ec076 100644
--- a/tests/iodef.xml
+++ b/tests/iodef.xml
@@ -46,5 +46,6 @@
         <Description>Confirm the source and take machines off-line and remediate</Description>
       </Expectation>
     </EventData>
+    <AdditionalData dtype="string" meaning="IODEF Test">Some additional data</AdditionalData>
   </Incident>
 </IODEF-Document>