Notation query in Mathematica: Re'

Question

In Mathematica (or WA) I'm seeking

$$\text{D[b*Abs[Exp[i*m/b*t]], t]}$$

and the result is

$$i m e^{\Re\left(\frac{i m t}{b}\right)} \text{Re}'\left(\frac{i m t}{b}\right).$$

I don't understand the meaning or significance of $\text{Re}'$.

Answer 1

It's derivative. Try Head[Re'] (but copy the Re' from your code, not from here). The output is Derivative[1].