PR #5728 Support syntactically directly nested list, enum, and term list

Optimized the syntax for nested list, enum, and terms elements.

Previously, to create nested elements, we had to use line breaks and indentation, like this:

1
+ first main
2
+
3
  - first sub
4
  - second sub

Now, the extra line break is no longer needed:

1
+ first main
2
+ - first sub
3
  - second sub