Question

These objects are newly defined objects needed for supporting the full connectivity through ports where the ports are vpiInterface or vpiModport or any object inside modport or interface.

RefObjs are dummy objects and they always have a handle to the original object.

interface simple ()
    logic req, gnt;
    modport slave (input req, output gnt);
    modport master (input gnt, output req);
}

module top()
    interface simple i;
    child1 i1(i);
    child2 i2(i.master);
endmodule

/***********************************
for port of i1,
    vpiHighConn = vpiRefObj where vpiRefObjType = vpiInterface

for port of i2 ,
    vpiHighConn = vpiRefObj where vpifullType = vpiModport
****************************************/
module child1(interface simple s)
    c1 c_1(s);
    c1 c_2(s.master);
endmodule

/****************************
for port of child1,
    vpiLowConn = vpiRefObj where vpiRefObjType = vpiInterface

for that refObj,
    vpiPort is = port of child1.

vpiPortInst is = s, s.master
vpiActual is = i.

for port of c_1 :
    vpiHighConn is a vpiRefObj, where full type is vpiInterface.

for port of c_2 :
    vpiHighConn is a vpiRefObj, where full type is vpiModport.