When presenting a technical derivation within a `"Section"` of a *Mathematica* notebook, I often encounter the situation where a lot of "details" separate equations `(n)` and `(n+1)`, and I suspect many readers would prefer not to see these details. I could use a collapsible `"Subsection"` to hold the required material, but at the end of the subsection I would have to create a new `"Section"` to continue the main flow of the document. I find this to be stylistically awkward. 

Have any of the wizards solved this sort of problem? Perhaps by developing a Style for a special section that can be collapsed or expanded in a standalone manner that doesn't interrupt the flow of the main document?