4 - String: Implement String != regex operator
5 - String: index and rindex methods with String argument
6 - String: format operator % like in python
7 - String: assign fstream objects to read and write a file
8 - String: convert to and from std::sstream and std::string
9 - regex: throw an exception when contructing a regex returns an error
11 - date: test parser for invalid dates and syntax errors
12 - date: Parser for stream input
13 - date: Yearday, Weekday and week number
15 - UTC: Convert to and from struct tm
17 - xml: Add access to attributes
18 - xml: Xinclude processing