In Cocoa applications (for instance, TextEdit) there used to be a completion functionality by which, pressing the esc, or ⌥+esc (apparently, it depends on Mac OS X versions), a list of possible completions for the word being typed appears. In latest versions, up to El Capitan, it worked with just esc; in macOS Sierra, apparently, it has been reverted to ⌥+esc.
Although I know that someone didn't like the use of just ESC, I found it very handy. Is there a way to enable it?
I tried defining it in System Preference > Keyboard > Shortcuts > App Shortcuts, but it seems not to accept esc alone as a shortcut.