Alright, this is very much “solely so it’s easy for me to find it”.
For lots of string formatting, Go by Example has a long set of examples. But the thing I’m probably thinking of is:
Which “prints a Go syntax representation of the value, i.e. the source code snippet that would produce that value.”
Percent-Pound-v (and don’t forget a newline).
Handy for “I want to see all the things going in in this variable” when poking around and debugging.