Folding inner nodes in navigation tree

[moretea]

Dear document writers,

First of all: you've done an amazing job so far!

May I suggest that we'd add a way to collapse (sub) chapters in the navigation tree? This would make it easier to discover chapters that one would like to read next.

I've opened an issue at mdBook https://github.com/azerupi/mdBook/issues/187 to ask for this feature.

[steveklabnik]

Thanks @moretea ! I'm going to close this issue in favor of that one; this really isn't up to us, it's up to mdBook.