Now a days I am studying Srednicki's QFT book. In its third chapter it is written that
Any local function of φ(x) is a Lorentz scalar, [...] .
Now my question is: What is a local function?
1) Well, the notion of locality depends on context. Usually in the context of QFT, a local function means a function of the form
$$ f(\varphi(x), \partial\varphi(x), \partial^2\varphi(x), \ldots,\partial^N\varphi(x) ;x), $$
2) Concretely, in the mentioned place almost at the end of chapter 3 in Srednicki's book, the phrase
is used (in a non-standard way) to denote
as opposed to, e.g.,