In some programming languages (e.g. C#, Visual Basic) there are language constructs that have no effect on the execution of code whatsoever, but exist solely to allow grouping fragments of code into regions (that can be nested, and can have captions). A region can be easily collapsed or expanded in most GUI code editors supporting these languages. The collapsed form displays only the caption of the region inline, but can also display the content summary in a tooltip when hovered by the mouse pointer. Regions sometimes are useful to see a high-level structure of code, while working on a particular piece within a single expanded region.
Question: Is there a similar feature in Mathematica?