code: public boolean isValidSubset(FieldSet set) {
  		if (set.size() > size()) {
  			return false;
  		}
  		for (Integer i : set) {
  			if (!contains(i)) {
  				return false;
  			}
  		}
  		return true;
  	}
docs: Checks if the given set of fields is a valid subset of this set of fields. For unordered
  sets, this is the case if all of the given set's fields are also part of this field.
  <p>
  Subclasses that describe field sets where the field order matters must override this method
  to implement a field ordering sensitive check.
  
  @param set The set that is a candidate subset.
  @return True, if the given set is a subset of this set, false otherwise.