code: protected Collection<String> filterIdentifiers(Collection<String> identifiers) {
  
          // Obtain enough space for a full copy of the given identifiers
          Collection<String> validIdentifiers = new ArrayList<String>(identifiers.size());
  
          // Add only valid identifiers to the copy
          for (String identifier : identifiers) {
              if (isValidIdentifier(identifier))
                  validIdentifiers.add(identifier);
          }
  
          return validIdentifiers;
  
      }
docs: Filters the given collection of strings, returning a new collection
  containing only those strings which are valid identifiers. If no strings
  within the collection are valid identifiers, the returned collection will
  simply be empty.
  
  @param identifiers
  The collection of strings to filter.
  
  @return
  A new collection containing only the strings within the provided
  collection which are valid identifiers.