Advanced Features in 5.10

1. Advanced Features
2. defined or
3. Turn on features explicitly
4. say
5. feature is a lexical pragma
6. static variable (with scope)
7. state variable
8. regex: Named capture buffers
9. Possessive quantifier
10. smartmatch ~~ - Don't use it!
11. Smart match example - Don't use it!
12. switch - Don't use it!