lib/Ext/navigation/View.js
function() {
        if (!this.$backButtonContainer) {
            return;
        }
        var i = 0,
            backButtonContainer = this.$backButtonContainer,
            items = backButtonContainer.items,
            item;

        for(;i < items.length; i++) {
            item = items.get(i);
            if(!item.isHidden()) {
                this.$backButtonContainer.show();
                return;
            }
        }

        this.$backButtonContainer.hide();
    }
function() {
        if (!this.$backButtonContainer) {
            return;
        }
        var i = 0,
            backButtonContainer = this.$backButtonContainer,
            items = backButtonContainer.items,
            item;

        for(;i < items.length; i++) {
            item = items.get(i);
            if(!item.isHidden()) {
                this.$backButtonContainer.show();
                return;
            }
        }

        this.$backButtonContainer.hide();
    }
This is used for Blackberry SplitNavigation to monitor the state of child items in the bottom toolbar.
if no visible children exist the toolbar will be hidden
@private