Add version disclaimer for Action Variables

Author: weirdwater

content/en/docs/apidocs-mxsdk/apidocs/studio-pro-10/pluggable-widgets/pluggable-widgets-client-apis/_index.md

@@ -88,6 +88,10 @@ onClick.execute({
 });
 ```
 
+{{% alert color="info" %}}
+Action Variables were introduced in Mendix [10.21](/releasenotes/studio-pro/10.21/#pluggable-widget-api-action-variables). Earlier versions of Mendix take 0 arguments for `execute()` and don't offer a direct way to pass variables to actions. Instead, use [attribute properties](/apidocs-mxsdk/apidocs/pluggable-widgets-property-types-10/#attribute) to set relevant values before calling `execute()`.
+{{% /alert %}}
+
 ### DynamicValue {#dynamic-value}
 
 `DynamicValue` is used to represent values that can change over time and is used by many property types. It is defined as follows:

content/en/docs/apidocs-mxsdk/apidocs/studio-pro-10/pluggable-widgets/pluggable-widgets-property-types.md

@@ -487,7 +487,11 @@ When a `dataSource` attribute is specified and configured by the user, it is pas
 
 #### XML Elements {#action-xml-elements}
 
-`<actionVariables>` — Defines variables a widget provides when calling [execute() on an ActionValue](/apidocs-mxsdk/apidocs/pluggable-widgets-client-apis/#execute). The variables are made available in Studio Pro when configuring [Call a Microflow](/refguide/on-click-event/#call-microflow) and [Call a Nanoflow](/refguide/on-click-event/#call-nanoflow) actions.
+{{% alert color="info" %}}
+Action Variables were introduced in Mendix [10.21](/releasenotes/studio-pro/10.21/#pluggable-widget-api-action-variables).
+{{% /alert %}}
+
+`<actionVariables>` — Defines variables a widget provides when calling [execute() on an ActionValue](/apidocs-mxsdk/apidocs/pluggable-widgets-client-apis-10/#execute). The variables are made available in Studio Pro when configuring [Call a Microflow](/refguide/on-click-event/#call-microflow) and [Call a Nanoflow](/refguide/on-click-event/#call-nanoflow) actions.
 
 `<actionVariable>` (required one or more) — Represents a primitive value provided by the widget as an argument when calling `ActionValue.execute()`. The variable is defined by the following attributes: