Code Folding / Unfolding (also called code collapsing) greatly adds to the organization and readability of documents you are working on. Big chunks of code that you have completed make it harder to locate the code you wish to edit and can be distracting. In this case, code folding makes your editing a lot easier.
With a single click you can collapse or expand all the folds in your document.
Example: Folded function (the '+' button unfolds it).
Example: The same function unfolded.
Example: Folded multi-line comment
Example: Unfolded multi-line comment
How? Simply highlight the code you wish to fold and select Fold selection. Give your fold a name to better organize your code. This way you can collapse a file of several thousand lines of code into few well-chosen folds: