diff --git a/Documentation/Configuration.rst b/Documentation/Configuration.rst
index 988ae99..4b0cec4 100644
--- a/Documentation/Configuration.rst
+++ b/Documentation/Configuration.rst
@@ -25,6 +25,10 @@ TCA, where data should be written to.
 In addition, you can define multiple ``columns`` as key-value pairs that will be added to the form
 input. This allows you to define the storage ``pid`` or hide new records.
 
+Both, table and columns, have to exist in the actual database and TCA. Otherwise they will not be
+inserted and no error is raised. If you need to insert "hidden" fields not visible inside of the
+backend, don't add them to ``showitem`` list.
+
 Example:
 
 .. literalinclude:: Examples/full.ts