$foo$ reference between checkbox to implement a "check All"/"uncheck All" checkbox

Hello!

I'm currently handling a set of 6 checkbox module. I would like to have a parent checkbox to "check all" the 6 children when checked and "uncheck all" when unchecked.

This is my try so far:

<module name="Checkbox" layoutPanel="panel_row2_col1">
                    <param name="name">parentbox</param>
                    <param name="label">parent box</param>
                    <param name="onValue">True</param>
                    <param name="offValue">False</param>
                    <param name="checked">True</param>

                    <module name="Checkbox" layoutPanel="panel_row2_col2">
                        <param name="name">childrenbox1</param>
                        <param name="label">param 1</param>
                        <param name="onValue">value1</param>
                        <param name="labelPosition">Right</param>
                        <param name="checked">$parentbox$</param>
                        <param name="float">left</param>

                    <module name="Checkbox" layoutPanel="panel_row2_col2">
                        <param name="name">childrenbox2</param>
                        <param name="label">param 2</param>
                        <param name="onValue">value2</param>
                        <param name="labelPosition">Right</param>
                        <param name="checked">$parentbox$</param>
                        <param name="float">left</param>    
...
But it is not responding as expected. It just gets ignored. I've tried with $parentbox$, $parentbox.value$, $parentbox.rawValue$ with no luck. However, the variable value is properly shown and updated when ticking the parent box inside a HTML module...

Any thoughts?

Thank you!!