Where were two of Donatello's characteristic formal contributions encountered? How did he demonstrate these?

The two Donatello's characteristic formal contributions are encountered in the work for Baptistery of Siena. He demonstated it through organizing the relief by a rigorous application of the rules of perspective. Even though it was created at a shallow deptht, this technique makes each figure of a scene emerge clearly and very logically. This technique is determined as a flattened relief.