Request: support for sub-sections

[TxHawks]

I'd like to be able to nest sections.

Say i have Foo section, using BEM in my css, I'd like to be able to group all of foo's modifier classes in a subsection of foo and all of its element classes in another subsection, both under the Foo section, and separate from other top-level sections.

If this is currently possible, I'm not sure how to achieve this

[stephenway]

@TxHawks How do you envision the UI for this feature?