Refs #11998 - Add explanation to qfq function example code.

Documentation/Report.rst

@@ -1948,14 +1948,15 @@ QFQ Function
 QFQ SQL reports can be reused, similar to a function in a regular programming language, including call parameter and return
 values.
 
-* Per tt-content record the field 'subheader' (in Typo3 backend) has to be used to define the function name. The function
+* Per tt-content record the field 'subheader' (in Typo3 backend) defines the function name. The function
   can also referenced by using the tt-content number (`uid`) - but this is less readable.
 * The calling report calls the function by defining ``<level>.function = <function name>(var1, var2, ...) => return1, return2, ...``
 * STORE_RECORD will be saved before calling the function and will be restored when the function has been finished.
-* Exception: the defined function call parameter and function return values will be filled and processed via STORE_RECORD.
-* Inside the QFQ function, all STORES are available.
+* The function has only access to STORE_RECORD variables which has been explicitly defined in the braces (var1, var2, ...).
+* The function return values will be copied to STORE_RECORD after the function finished.
+* Inside the QFQ function, all other STORES are fully available.
 * If ``<level>.function`` and ``<level>.sql`` are both given, ``<level>.function`` is processed first.
-* If ``<level>.function`` is given, but ``<level>.sql`` not, the values of ``shead, stail, althead`` are processed.
+* If ``<level>.function`` is given, but ``<level>.sql`` not, the values of ``shead, stail, althead`` are even processed.
 * If a function outputs something, this is *not* shown.
 * The output of a QFQ function is accessible via ``{{_output:R}}``.
 * It is possible to call functions inside of a function.
@@ -1969,7 +1970,7 @@ Example tt-content record for the function::
         #
         render = api
 
-        10 {
+        100 {
           sql = SELECT p.firstName AS _firstName
                        , NOW() AS now, CONCAT('p:{{pageAlias:T}}&form=person&r=', p.id ) AS '_pagee|_hide|myLink'            
                   FROM Person AS p
@@ -2003,6 +2004,15 @@ Example tt-content record for the calling report::
       }
     }                                                                    
 
+Explanation:
+
+* Level 10 iterates over all `person`.
+* Level 10.20 calls QFQ function `getFirstName()` by delivering the `pId` via STORE_RECORD. The function expects the return
+  value `firstName` and `myLink`.
+* The function selects in level 100 the person given by ``{{pId:R}}``. The `firstName` is not printed but a hidden column.
+  Column ``now`` is printed. Column 'myLink' is a rendered link, but not printed.
+* Level 10.30 prints the return values ``firstName`` and ``myLink`` (as rendered link and as source definition). The last
+  column is the output of the function - the value of ``NOW()``
 
 .. _download: