Multilevel checklists
From Planfix
You can create a multilevel checklist using the corresponding checklist menu item or hotkeys:
As a result, you get a multilevel checklist:
Collapsing and expanding multilevel checklists
Multilevel checklists can be collapsed or expanded by clicking the triangle next to the checklist item name:
Checklists may contain dozens of items, so having the ability to collapse them can come in handy. A large multilevel checklist can be collapsed to the highest level, which provides a convenient and compact view. Then, items can be expanded as needed: