Either EMA or XAvg can be used as the name of this function.
Count is usually thought of as an integer representing a number of bars, but can actually be any decimal value. An EMA is constructed by multiplying each difference between the result so far and the next value by a factor equal to 2 / (count + 1).
Note that, like most other backtesting software, RealTest begins each EMA calculation with MA(expr, count), then begins to apply the EMA weighting for subsequent bars once count has been reached.