docs: public static void deleteContentsInDirectoryTree(File root, String includeMask) {
  		Collection<File> files = getContentsInDirectoryTree(root, includeMask, true, true);
  		for(File file : files) {
  			if (file.exists()) {//file may meanwhile have been deleted
  				if (file.isDirectory()) {
  					//empty directory
  					emptyDirectory(file.getAbsolutePath());
  				}
  				file.delete();				
  			}
  		}
  	}