Index.rst: describe how to ommit a preselection on Radios

extension/Documentation/UsersManual/Index.rst

@@ -1168,6 +1168,16 @@ Type: radio
   * *emptyHide*: Existence of this item hides the empty entry. This is useful for e.g. Enums, which have an empty
     entry but the empty value should not be an option to be selected.
 
+* No preselection:
+
+  * If there is a default configured on a table column, such a value is selected by default. If the user should actively
+    choose an option, the 'preselection' can be omitted by specifying an explicit definition on the FormElement field `value`::
+
+      {{<columnname>:RZ}}
+
+    For existing records the shown value is as expected the value of the record. For new records, it's the value `0`,
+    which is typically not one of the ENUM values and therefore nothing is selected.
+
 Type: select
 ^^^^^^^^^^^^