cdm/src/main/java/ucar/nc2/ncml/Aggregation.java
public void addCollection(String spec, String olderThan) throws IOException {
    datasetManager = MFileCollectionManager.open(spec, spec, olderThan, new Formatter());
 }
public void addCollection(String spec, String olderThan) throws IOException {
    datasetManager = MFileCollectionManager.open(spec, spec, olderThan, new Formatter());
 }
experimental