Exponent operation over element of G I found a definition of an exponent operation over the element of $\mathbb{G}$ in this paper (page 4):

$$ (g^a)^{\% b} = g ^{a \text{ mod } b}$$

I couldn't understand the rest of the paper (Decrypt primitive).

We have $D = g^r g^{M_S} = g^{r + M_S}$

How could they compute: $(D)^{\% M_T}$. In this paper, they have written it in a form: 

$$(D)^{\% M_T} = g^{(r + M_S) \text{ mod } M_T}$$

But the exponentiation in $D$ is already computed, we cannot run the $\text{ mod }$ operator before the exponentiation.

Here are captures of the paper:





Thank you in advance for your help.
Assuming that $M_T$ is the order of $g$, then it's real easy to compute $(D)^{\%M_T}$: it's the value $D$.

That is, if $M_T$ is the order of $g$, then we have the identity $g^x = g^{x \bmod M_T}$ for any $x$, and in particular, $g^{r + M_S} = g^{(r + M_S) \bmod M_T}$.

The paper is just noting that the $\bmod$ operation happens implicitly here.

BTW: I've never seen the notation $(g^a)^{\%b}$ before; I don't believe that's very standard...