What do you mean by using it in "real time"?
Suppose there is a function avg(). As a real time example, I can say that if i want the sales of a region for a year on an average, I will be using this function. In a similar way I wanted to know about attr(). I am not able to understand any such scenario where we have to use it in real time
ATTR() gets the specific value on a row-by-row basis.