Programmatically access a declarative ToggleButton

I've just started with Dojo/Javascript and even though I kind of understand all the AMD way of coding, I keep getting stuck on these (probably) easy things: how can I programmatically access a widget created in a declarative way?

I have a toggle button created like this:

<button id="toggleLeg" data-dojo-type="dijit/form/ToggleButton" data-dojo-props="iconClass:'dijitCheckBoxIcon', checked: true, onChange: function(value){legendVisibility(value);}">Legend/Layers</button>

And I would like to call the legendVisibility() function when clicking on it using the true/false returning values from the button.

The function simply toggle an accordion container on and off using its CSS property (the accordion is included into a content pane with id="legPanel").

    function legendVisibility(value) {
        checked = value;
        var rightPane = dom.byId('legPanel');
        if (checked == false) {
            //I want the right pane out
            domStyle.set(rightPane , 'display', 'none');
        } else {
            //I want the right pane in (preserving its content)
            domStyle.set(rightPane , 'display', 'block');
        }
    }

If I put it outside the main require function it clearly throws a ReferenceError saying that "dom is not defined" when declaring the var rightPane.

How can I correctly include it into the require function and programmatically use the widget?

Should I get rid of the onChange: function(value){legendVisibility(value);} when creating the widget?

The modules I need are "dojo/dom" to get the reference of the node and "dojo/dom-style" to change the CSS properties. Do I need the "dojo/on" too to use the event propagated by the click? (I also tried with the Toggler function with no luck!)

Thanks in advance,

mic