I'd like a conditional formatting rule to mark cells with formulas one way, and cells with user-typed values instead of formulas another way. This way you can quickly see which cells are filled by formulas and which are not.
For example (this is a trivial, made-up example to make my point): a cell contains a 1 in it. I want it bold if that 1 comes from some formula, like =if(A1=today(), 1, 0), and I want it not bold if the user actually just typed a 1 into the cell. Make sense?
Again, I'm looking for a general-purpose way to identify formula-filled vs user-typed cells.
I am unable to figure it out. Choosing the "Custom formula is" allows you to enter a custom formula to run, rather than matching if a custom formula exists in that cell.
See also: Google's help: Use conditional formatting rules in Google Sheets