What does the "data.table" package's syntax "DT[, newcol := value]" do compared to base R or dplyr equivalents?

A It creates a new copy of DT with an added column, like base R assignment B It modifies DT in place (by reference) to add or update "newcol", avoiding the overhead of copying the entire table C It deletes the column newcol D It is identical to "DT$newcol <- value" in terms of performance