Notation in Belavin-Drinfeld's classification of solutions to classical Yang-Baxter equations.

Question

I am reading the paper, on page 6, equation (3.5), there is a notation $(1 \otimes \alpha)r_0$, where $r_0 \in g \otimes g$, $g$ is a semisimple Lie algebra, $\alpha$ is a root. For example, suppose that $r_0 = E \otimes F$ in the case of $sl_2$. What is $(1 \otimes \alpha)(E \otimes F)$? I think that we have $(1 \otimes \alpha)(E \otimes F) = E \otimes \alpha(F)$. But what is $\alpha(F)$? Thank you very much.