diff --git a/Classes/Core/Model/AbstractBaseType.php b/Classes/Core/Model/AbstractBaseType.php
index abaf9ff6..b1ab2663 100644
--- a/Classes/Core/Model/AbstractBaseType.php
+++ b/Classes/Core/Model/AbstractBaseType.php
@@ -13,6 +13,7 @@
 
 /**
  * This class provides the logic for both, a single type and a multiple type.
+ * It is not for use in custom extensions. Use AbstractType instead.
  *
  * @internal
  */
@@ -33,7 +34,7 @@ abstract class AbstractBaseType implements TypeInterface
      */
     protected array $properties = [];
 
-    public function setId($id): self
+    public function setId($id): static
     {
         if (! $this->isValidDataTypeForId($id)) {
             throw new \InvalidArgumentException(
@@ -84,7 +85,7 @@ public function hasProperty(string $propertyName): bool
         return true;
     }
 
-    public function getProperty(string $propertyName)
+    public function getProperty(string $propertyName): mixed
     {
         $this->checkPropertyExists($propertyName);
 
@@ -106,7 +107,7 @@ private function checkPropertyExists(string $propertyName): void
         }
     }
 
-    public function setProperty(string $propertyName, $propertyValue): self
+    public function setProperty(string $propertyName, $propertyValue): static
     {
         $propertyValue = $this->stringifyNumericValue($propertyValue);
         $this->checkProperty($propertyName, $propertyValue);
@@ -165,7 +166,7 @@ private function isValidDataTypeForPropertyValue(mixed $propertyValue): bool
             || $propertyValue instanceof EnumerationInterface;
     }
 
-    public function addProperty(string $propertyName, $propertyValue): self
+    public function addProperty(string $propertyName, $propertyValue): static
     {
         $propertyValue = $this->stringifyNumericValue($propertyValue);
         $this->checkProperty($propertyName, $propertyValue);
@@ -194,7 +195,7 @@ public function addProperty(string $propertyName, $propertyValue): self
         return $this;
     }
 
-    public function setProperties(array $properties): self
+    public function setProperties(array $properties): static
     {
         foreach ($properties as $propertyName => $propertyValue) {
             $this->setProperty($propertyName, $propertyValue);
@@ -203,7 +204,7 @@ public function setProperties(array $properties): self
         return $this;
     }
 
-    public function clearProperty(string $propertyName): self
+    public function clearProperty(string $propertyName): static
     {
         $this->checkPropertyExists($propertyName);
 
diff --git a/Classes/Core/Model/TypeInterface.php b/Classes/Core/Model/TypeInterface.php
index 07276c24..c54cf5c5 100644
--- a/Classes/Core/Model/TypeInterface.php
+++ b/Classes/Core/Model/TypeInterface.php
@@ -17,7 +17,8 @@ interface TypeInterface extends NodeIdentifierInterface
      * Set the id.
      *
      * @param NodeIdentifierInterface|string|null $id The id
-     * @return self
+     * @return static
+     * @todo Declare return type in method with v4.0.0
      */
     public function setId($id);
 
@@ -33,6 +34,7 @@ public function hasProperty(string $propertyName): bool;
      *
      * @param string $propertyName The property name
      * @return mixed
+     * @todo Declare return type in method with v4.0.0
      */
     public function getProperty(string $propertyName);
 
@@ -41,7 +43,8 @@ public function getProperty(string $propertyName);
      *
      * @param string $propertyName The property name
      * @param mixed $propertyValue The value of the property
-     * @return self
+     * @return static
+     * @todo Declare return type in method with v4.0.0
      */
     public function setProperty(string $propertyName, mixed $propertyValue);
 
@@ -50,7 +53,8 @@ public function setProperty(string $propertyName, mixed $propertyValue);
      *
      * @param string $propertyName The property name
      * @param mixed $propertyValue The property value
-     * @return self
+     * @return static
+     * @todo Declare return type in method with v4.0.0
      */
     public function addProperty(string $propertyName, mixed $propertyValue);
 
@@ -62,7 +66,8 @@ public function addProperty(string $propertyName, mixed $propertyValue);
      * value = property value
      *
      * @param array<string, mixed> $properties
-     * @return self
+     * @return static
+     * @todo Declare return type in method with v4.0.0
      */
     public function setProperties(array $properties);
 
@@ -70,7 +75,8 @@ public function setProperties(array $properties);
      * Clear a property.
      *
      * @param string $propertyName The property name
-     * @return self
+     * @return static
+     * @todo Declare return type in method with v4.0.0
      */
     public function clearProperty(string $propertyName);
 
diff --git a/Documentation/Developer/Api.rst b/Documentation/Developer/Api.rst
index 4c91ca0c..3d887bd0 100644
--- a/Documentation/Developer/Api.rst
+++ b/Documentation/Developer/Api.rst
@@ -285,10 +285,11 @@ class.
 Available type model methods
 ----------------------------
 
-The type models which extend :php:`\Brotkrueml\Schema\Core\Model\AbstractType`
-expose the following methods:
+The type models which implement :php:`\Brotkrueml\Schema\Core\Model\TypeInterface`
+or extend :php:`\Brotkrueml\Schema\Core\Model\AbstractType` expose the following
+methods:
 
-.. confval:: setId($id)
+.. confval:: setId($id): static
    :name: abstracttype-setid
 
    The method sets the unique ID of the model. With the ID, you can
@@ -322,7 +323,7 @@ expose the following methods:
       A previously set ID or null (if not defined).
 
 
-.. confval:: setProperty($propertyName, $propertyValue)
+.. confval:: setProperty($propertyName, $propertyValue): static
    :name: abstracttype-setproperty
 
    Call this method to set a property or overwrite a previously one.
@@ -340,7 +341,7 @@ expose the following methods:
       Reference to the model itself.
 
 
-.. confval:: addProperty($propertyName, $propertyValue)
+.. confval:: addProperty($propertyName, $propertyValue): static
    :name: abstracttype-addproperty
 
    Call this method if you want to add a value to an existing one. In the
@@ -364,7 +365,7 @@ expose the following methods:
       Reference to the model itself.
 
 
-.. confval:: setProperties($properties)
+.. confval:: setProperties($properties): static
    :name: abstracttype-setproperties
 
    Set multiple properties at once.
@@ -379,7 +380,7 @@ expose the following methods:
       Reference to the model itself.
 
 
-.. confval:: getProperty($propertyName)
+.. confval:: getProperty($propertyName): mixed
    :name: abstracttype-getproperty
 
    Get the value of a property.
@@ -394,7 +395,7 @@ expose the following methods:
       strings, array of models, null).
 
 
-.. confval:: hasProperty($propertyName)
+.. confval:: hasProperty($propertyName): bool
    :name: abstracttype-hasproperty
 
    Check whether the property name exists in a particular model.
@@ -407,7 +408,7 @@ expose the following methods:
       :php:`true`, if the property exists and :php:`false`, otherwise.
 
 
-.. confval:: clearProperty($propertyName)
+.. confval:: clearProperty($propertyName): static
    :name: abstracttype-clearproperty
 
    Resets the value of the property (set it to :php:`null`).
@@ -421,7 +422,7 @@ expose the following methods:
       Reference to the model itself.
 
 
-.. confval:: getPropertyNames()
+.. confval:: getPropertyNames(): array
    :name: abstracttype-getpropertynames
 
    Get the names of all properties of the model.
@@ -430,7 +431,7 @@ expose the following methods:
       Array of all property names of the model.
 
 
-.. confval:: getType()
+.. confval:: getType(): string|string[]
    :name: abstracttype-gettype
 
    Get the type of the model.