Add missing "from-version" tags to new features

editions/tw5.com/tiddlers/filters/getvariable.tid

@@ -8,7 +8,7 @@ op-input: a selection of varible names
 op-parameter: ignored
 op-output: the values of each of the variables named in the input titles (or blank if the variable is not defined)
 
-The usual way to retrieve a variable value within a filter is with the angle brackets notation. For example, `[<currentTiddler>]` will retrieve the value of the variable called `currentTiddler`. 
+|<<.from-version "5.1.20">> The usual way to retrieve a variable value within a filter is with the angle brackets notation. For example, `[<currentTiddler>]` will retrieve the value of the variable called `currentTiddler`. 
 
 The `getvariable` filter operator provides an alternative way to retrieve a variable. For example, `[[currentTiddler]getvariable[]]` is another way to retrieve the value of the variable `currentTiddler`.
 

editions/tw5.com/tiddlers/filters/variables.tid

@@ -9,7 +9,7 @@ op-input: ignored
 op-parameter: none
 op-output: the names of all the actively defined variables
 
-The primary purpose of the `variables` operator is to implement the [[dumpvariables Macro]]:
+<<.from-version "5.1.20">> The primary purpose of the `variables` operator is to implement the [[dumpvariables Macro]]:
 
 <$codeblock code={{$:/core/macros/dumpvariables}}/>