editmesh_bevel.c:

void MESH_OT_bevel(wmOperatorType *ot)
{
  ...

  RNA_def_pointer(ot->srna, "prwdgt", "ProfileWidget", "", "Widget for editing profile path");
  ...
}

static bool edbm_bevel_calc(wmOperator *op)
{
  ...
  const PointerRNA prwdgt_ptr = RNA_pointer_get(op->ptr, "prwdgt");
  ...
}