Mixing `-` and `*` lists causes omissions

[djmitche]

https://github.com/taskchampion/taskchampion/pull/220/files#diff-6e490221db20aaa056f2ed2c63443806b309ec63182541ddea9dd0b84e7eb501R4 changed SUMMARY.md:

- [Welcome to TaskChampion](./welcome.md)
  - [Installation](./installation.md)
  * [Using the Task Command](./using-task-command.md)

to

- [Welcome to TaskChampion](./welcome.md)
  * [Installation](./installation.md)
  * [Using the Task Command](./using-task-command.md)

before this change, the installation chapter did not appear in the TOC, nor did it get generated into HTML.

I suspect there's an issue with mixing - and *. I admit it's a weird way to write a list, but the docs do say that either one can be used. At least, it'd be nice if this was flagged as an error in mdbook test.

[joshrotenberg]

Quick guess here ... the parser is following the CommonMark spec. The list section of the spec says:

A list is a sequence of one or more list items of the same type.

The same type part is key, because it means that a list item that starts with a different delimiter is technically the start of a new list. See Example 271:

So this markdown ...

- foo
- bar
+ baz

Results in this html:

<ul>
<li>foo</li>
<li>bar</li>
</ul>
<ul>
<li>baz</li>
</ul>

My assumption is that in the mdbook implementation, we (correctly) see the end of the list because the delimiter changes and end the parsing of the indented section.

[djmitche]

That makes sense!

I'd expect to either see it at the top level, or in a new anonymous indented section, or an error message.

[joshrotenberg]

I'd expect to either see it at the top level, or in a new anonymous indented section, or an error message.

Given that the SUMMARY.md is intended to have a stricter than normal Markdown syntax specific to it's purpose for mdbook I think an error is the right way to go unless there is a feature related reason to allow multiple lists at the same indentation level. In the meantime I added a note to the documentation.

[frewsxcv]

Does our commonmark parser inform us that there is a mixing of symbols?