@Override
    public void freeze() {
        if (isFrozen()) return;

        for (PageElement element : elements)
            element.freeze();
        elements=Collections.unmodifiableList(elements);
        sections=createElementList(Section.class);
        sources=createElementList(Source.class);
        renderers=createElementList(Renderer.class);

        super.freeze();
    }
Returns min number of (immediate) elements/sections desired within this, -1 means unrestricted. Default: -1.
container-search/src/main/java/com/yahoo/search/pagetemplates/model/Section.java