public void setRendererFor(String rendererFor) {
        ensureNotFrozen();
        this.rendererFor=rendererFor;
    }
Returns the name of the kind of data this is a renderer for.
This is used to allow frontends to dispatch the right data items (hits) to
the right renderer in the case where the data consists of a heterogeneous list.
<p>
This is null if this is a renderer for a whole section, or if this is a renderer
for all kinds of data from a particular source <i>and</i> this is not frozen.
<p>
Otherwise, it is either the name of the source this is the renderer for,
<i>or</i> the renderer for all data items having this name as a <i>type</i>.
<p>
This, a (frontend) dispatcher of data to renderers should for each data item:
<ul>
    <li>use the renderer having the same name as any <code>type</code> name set of the data item
    <li>if no such renderer, use the renderer having <code>rendererFor</code> equal to the data items <code>source</code>
    <li>if no such renderer, use a default renderer
</ul>
container-search/src/main/java/com/yahoo/search/pagetemplates/model/Renderer.java