DOC: Extend documentation for variable replacement in transformers

src/doc/converters/transform_functions.rst

@@ -38,8 +38,33 @@ An example that splits the variable ``a`` and puts the generated list in ``b`` i
 	  Report:
 	    tags: $b
 
-This splits the string in '$a' and stores the resulting list in '$b'. This is here used to add a
-list valued property to the Report Record.
+This splits the string in '$a' and stores the resulting list in
+'$b'. This is here used to add a list valued property to the Report
+Record. Note that from LinkAhead Crawler 0.11.0 onwards, the value of
+``marker`` in the above example can also be read in from a variable in
+the usual ``$`` notation:
+
+.. code-block:: yaml
+
+    # ... variable ``separator`` is defined somewhere above this part, e.g.,
+    # by reading a config file.
+    Experiment:
+	type: Dict
+	match: ".*"
+	transform:
+	  param_split:
+	    in: $a
+	    out: $b
+	    functions:
+	    - split:
+		marker: $separator  # Now the separator is read in from a
+				    # variable, so we can, e.g., change from
+				    # '|' to ';' without changing the cfood
+				    # definition.
+	records:
+	  Report:
+	    tags: $b
+
 
 
 There are a number of transform functions that are defined by default (see