Moved the region's add method to the general container abstraction since such
functionality is useful for other nodes such as table cells provided by the
table parser.
1 XXX
2 * Item 1
3 * Item 1.1
4 * Item 2
5 . Item 3
6 . Item 3.1
7 . Item 3.1.1
8 * Item A
9 XXX
10 * Boring
11 * Flat
12 * List
13 XXX
14 * List with
15 continuation
16 * Continuing...
17 again
18 And stop.