code: public List<Extension> getExtensions () {
  		List<Extension> list = new ArrayList<Extension>();
  		for (AddOn addOn : getAddOnCollection().getAddOns()) {
  			list.addAll(getExtensions(addOn));
          }
  		
  		return list;
  	}
docs: Returns all the {@code Extension}s of all the installed add-ons.
  <p>
  The discovery of {@code Extension}s is done by resorting to the {@link AddOn#MANIFEST_FILE_NAME manifest file} bundled in
  the add-ons.
  <p>
  Extensions with unfulfilled dependencies are not be returned.
  
  @return a list containing all {@code Extension}s of all installed add-ons
  @since 2.4.0
  @see Extension
  @see #getExtensions(AddOn)