HLA example question?

Using the example AoA [12.4 Programming in C/C++ and HLA]:

unit ReturnHWUnit;

procedure ReturnHW; external( "_ReturnHW" );
procedure ReturnHW; nodisplay; noframe; noalignstk;

begin ReturnHW;

lea( eax, "Hello World" );

end ReturnHW;

end ReturnHWUnit;

I tried to compile using: "hla -c rhw.hla" and got:

linux:~/hla> hla -c rhw.hla
Error in file "t.hla" at line 4 [errid:99124/hlaparse.c]:
syntax error, unexpected UndefID.
Near: << nodisplay >>

If I comment out: "nodisplay; noframe; noalignstk;" (i.e., procedure
ReturnHW; //nodisplay; noframe; noalignstk;) it works. Why?

---Thanks for your time