[trentnelson]

I think that's referring to the prolog/epilog convention and "homing" of parameter registers, e.g.

Frame struct ReturnAddress dq ? HomeRcx dq ? HomeRdx dq ? HomeR8 dq ? HomeR9 dq ? Frame ends

    NESTED_ENTRY Foo, _TEXT$00

    mov Frame.HomeRcx[rsp], rcx
    mov Frame.HomeRdx[rsp], rcd
    mov Frame.HomeR8[rsp], r8
    mov Frame.HomeR9[rsp], r9

    alloc_stack 64

    END_PROLOG
    
    ; *do stuff*

    BEGIN_EPILOG

    add rsp, 64

    NESTED_END Foo, _TEXT$00

https://msdn.microsoft.com/en-us/library/tawsa7cb.aspx