Take what was input and treat it as an expression argument to dplyr function.
treat_input_as_expr(arg)the argument for which the literal input text is to be used as an expression.
something that will resolve to an expression when prefixed by `!!`
This is used inside a function to pass the literal text of what the caller typed as an expression to a `dplyr` function. These might be logical expressions passed to filter: `filter(dat, col == "example")`, or functions of columns passed to mutate or summarise: `summarise(dat, mean(col))`.