What is EOF!! in the bash script?

Question

There is a command I don\'t understand:

custom_command << EOF!!

I want to ask what EOF!! is in the bash script. I did find EOF with googl

Answer 1

The bash manual lists this under "Event designators", saying:

!!

Refer to the previous command. This is a synonym for !-1`.

I simply searched for "bash manual double exclamation".