Use ProMdlSetdatumtagCreate to add the reference symbol to the dimension annotations in the engineering drawing?

I want to add a reference symbol to a dimension annotation on the view in the engineering drawing, but I'm not sure what the correct way to do it is.

 

 ProSelection sel_dim = NULL;
 ProError err = ProSelectionAlloc(NULL, (ProModelitem*)&dim, &sel_dim);
 if (err != PRO_TK_NO_ERROR) {

     return;
 }

 ProSetDatumTag datum;
 err = ProMdlSetdatumtagCreate((ProMdl)drawing, sel_dim, NULL, L"A", &datum);
 if (err == PRO_TK_NO_ERROR) 
 {
     ProAnnotationShow((ProAnnotation*)&datum, NULL, RightView);
     ProWindowRepaint(PRO_VALUE_UNUSED);
 }
 ProSelectionFree(&sel_dim);