/**
* Save the given fragment in the cache. (Also registers as a DataListener on the appropriate
* rollup instance list, so it can invalidate this cache entry if the instance list changes.)
*/
public String put(String rollupID, String fragment) {
if (!contents.containsKey(rollupID))
data.addDataListener(rollupInstanceList(rollupID), this, false);
contents.put(rollupID, fragment);
return fragment;
}
