mixed together. Here is an example of right TOC:
```
- ------- TOC -------
- / \
- edition1 edition2
- | |
- -chapter1 -chapter3
- -chapter2
+------- TOC -------
+ / \
+ edition1 edition2
+ | |
+ -chapter1 -chapter3
+ -chapter2
```
Here are two editions (alternatives), the first contains two chapters
example of invalid TOC:
```
- ------- TOC -------
- / \
- edition1 chapter1
- |
- -chapter1
- -chapter2
+------- TOC -------
+ / \
+ edition1 chapter1
+ |
+ -chapter1
+ -chapter2
```
Here you have edition1 and chapter1 mixed on the same level of