“TST is literally the killer feature for FF …”
No - it is figuratively the killer feature.
If it were literally the killer function this would be a very different discussion.
No - it is figuratively the killer feature.
If it were literally the killer function this would be a very different discussion.
vs
> (literally the killer) feature
A "killer feature" is a phrase with its own meaning so we can treat it as an atom and apply modifiers to it. The order of operations matters, and I posit that the OP placed their imaginary parentheses as I did in my first example.