Great part of Blender's GUI is a terra icognita for me since I use it only for modelling. There are always functions that I didn't know about. That's why making icons is a kind of adventure - every day brings a surprise. Yesterday I discovered
Summary button
which makes
DopeSheet add an extra row with accumulation of all keys, actions and what not - pure essence of whole content, easy to take in.
Currently
Summary uses
Border Zoom icon {CA4}, but it doesn't reflect the functionality - I propose to use universal mathematical symbol usually used for summation.