A note on the centralizer of a subalgebra of the Steinberg algebra

For an ample Hausdorff groupoid $\mathcal{G}$, and the Steinberg algebra $A_R(\mathcal{G})$ with coefficients in the commutative ring $R$ with unit, we describe the centralizer of the subalgebra $A_R(U)$ with $U$ an open closed invariant subset of the unit space of $\mathcal{G}$. In particular, it is shown that the algebra of the interior of the isotropy is indeed the centralizer of the diagonal subalgebra of the Steinberg algebra. This will unify several results in the literature, and the corresponding results for Leavitt path algebras follow.