Notepad++

Expand/Collapse (folding)

In short:
Alt+0 folds (collapses) all Blocks
Alt+1 folds all Level 1
Alt+2 folds all Level 2
Alt+x etc.

and
Alt+Shift+0 Unfolds all
Alt+Shift+1 Unfolds Level 1
Alt+Shift+2 Unfolds Level 2
Alt+Shift+3 Unfolds Level 3
Alt+Shift+x etc.