The String class is not suported in PHP 7.

src/Account.php

@@ -3,7 +3,7 @@
 class Account extends Element {
   protected $props = [
     'homePage' => 'Locker\XApi\IRI',
-    'name' => 'Locker\XApi\String',
+    'name' => 'Locker\XApi\Str',
   ];
   protected $required_props = ['homePage', 'name'];
 }

src/Agent.php

@@ -6,7 +6,7 @@ class Agent extends Element {
   use TypedElement;
 
   protected $props = [
-    'name' => 'Locker\XApi\String',
+    'name' => 'Locker\XApi\Str',
     'mbox' => 'Locker\XApi\Mailto',
     'mbox_sha1sum' => 'Locker\XApi\Sha1',
     'openid' => 'Locker\XApi\IRI',

src/Attachment.php

@@ -7,7 +7,7 @@ class Attachment extends Element {
     'description' => 'Locker\XApi\LanguageMap',
     'contentType' => 'Locker\XApi\IMT',
     'length' => 'Locker\XApi\Integer',
-    'sha2' => 'Locker\XApi\String',
+    'sha2' => 'Locker\XApi\Str',
     'fileUrl' => 'Locker\XApi\IRI'
   ];
   protected $required_props = ['usageType', 'display', 'contentType', 'length', 'sha2'];

src/Context.php

@@ -6,8 +6,8 @@ class Context extends Element {
     'instructor' => 'Locker\XApi\Actor',
     'team' => 'Locker\XApi\Group',
     'contextActivities' => 'Locker\XApi\ContextActivities',
-    'revision' => 'Locker\XApi\String',
-    'platform' => 'Locker\XApi\String',
+    'revision' => 'Locker\XApi\Str',
+    'platform' => 'Locker\XApi\Str',
     'language' => 'Locker\XApi\Language',
     'statement' => 'Locker\XApi\StatementRef',
     'extensions' => 'Locker\XApi\Extensions'

src/InteractionComponent.php

@@ -2,7 +2,7 @@
 
 class InteractionComponent extends Element {
   protected $props = [
-    'id' => 'Locker\XApi\String',
+    'id' => 'Locker\XApi\Str',
     'description' => 'Locker\XApi\LanguageMap'
   ];
 }

src/LanguageMap.php

@@ -11,7 +11,7 @@ public function validate() {
       $errors = array_merge($errors, (new Language($set_prop))->validate());
       $errors = array_merge($errors, array_map(function ($error) use ($set_prop) {
         return $error->addTrace($set_prop);
-      }, (new String($this->value->{$set_prop}))->validate()));
+      }, (new Str($this->value->{$set_prop}))->validate()));
     }
     return array_merge($errors, parent::validate());
   }

src/ObjectDefinition.php

@@ -3,7 +3,7 @@
 class ObjectDefinition extends Definition {
   protected $props = [
     'interactionType' => 'Locker\XApi\InteractionType',
-    'correctResponsesPattern' => 'Locker\XApi\Strings',
+    'correctResponsesPattern' => 'Locker\XApi\Strs',
     'choices' => 'Locker\XApi\InteractionComponents',
     'scale' => 'Locker\XApi\InteractionComponents',
     'source' => 'Locker\XApi\InteractionComponents',

src/Result.php

@@ -5,7 +5,7 @@ class Result extends Element {
     'score' => 'Locker\XApi\Score',
     'success' => 'Locker\XApi\Boolean',
     'completion' => 'Locker\XApi\Boolean',
-    'response' => 'Locker\XApi\String',
+    'response' => 'Locker\XApi\Str',
     'duration' => 'Locker\XApi\Duration',
     'extensions' => 'Locker\XApi\Extensions',
   ];

src/String.php → src/Str.php

@@ -1,5 +1,5 @@
 <?php namespace Locker\XApi;
 
-class String extends TypedAtom {
+class Str extends TypedAtom {
   protected static $expected_types = ['string'];
 }

src/Strings.php

@@ -1,5 +1,5 @@
 <?php namespace Locker\XApi;
 
 class Strings extends Collection {
-  protected $member_type = 'Locker\XApi\String';
+  protected $member_type = 'Locker\XApi\Str';
 }