We define and study the Hodge stratification for the special fiber of Shimura varieties defined with the Pappas–Rapoport condition, in the case of low ramification index (e≤3). For e≤2, the Hodge polygon induces a strong stratification. For e=3, one needs to introduce several polygons. They describe the isomorphism class of the sheaf of differentials with extra structure, and induce a strong stratification on the variety.
Stéphane Bijakowski (Thu,) studied this question.