code: private boolean exclude(String identifier) {
      String excludeMatch = null;
      for (String rule = identifier; rule != null; rule = enclosing(rule)) {
        if (excludes.contains(rule)) {
          excludeMatch = rule;
        }
      }
      if (excludeMatch != null) {
        usedExcludes.add(excludeMatch);
        return true;
      }
      return false;
    }
docs: Returns true if {@code identifier} or any of its enclosing identifiers is excluded.