Add documentation for fieldControl -> rendertype

Documentation/Columns/_Properties/_Config.rst.txt

@@ -17,18 +17,18 @@
 
     ..  confval:: type
         :name: columns-config-type
+        :Type: string, one of the :ref:`column types <columns-types>`
         :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']['type']
         :Required: true
-        :type: string, one of the :ref:`column types <columns-types>`
 
         The `type` influences the rendering of the form field in the backend.
         It also influences the processing of data on saving the values.
 
     ..  confval:: rendertype
         :name: columns-config-rendertype
+        :Type: string
         :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']['rendertype']
         :Required: true
-        :type: string
 
         For some :confval:`columns-config-type` definitions there are additional
         render types available that mainly influence rendering. For example

Documentation/ColumnsConfig/Type/Group/_Properties/_FieldControl.rst.txt

@@ -88,6 +88,17 @@
         button to open an element browser. It is enabled by default if rendering a
         group element.
 
+        ..  confval:: rendertype
+            :name: group-fieldControl-elementBrowser-rendertype
+            :Type: string
+            :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']['rendertype']
+            :Required: true
+            :Default: elementBrowser
+
+            Use a render type from core or your own. Custom render types can be
+            registered with the `NodeFactory <https://docs.typo3.org/permalink/t3coreapi:FormEngine-Rendering-NodeFactory>`_.
+
+
     ..  confval:: insertClipboard
         :name: group-fieldControl-insertClipboard
         :Path: $GLOBALS['TCA'][$table]['columns'][$field]['config']['fieldControl']