Child, HGroup,
Child, TextObject, ButtonFrame,
MUIA_Background, MUII_TextBack,
MUIA_Text_Contents, "\33c Et ici un TextObject avec une frame
d'aspect \33iButtonFrame\33n\nce qui lui donne son aspect de bouton",
End,

Child, TextObject, StringFrame,
MUIA_Background, MUII_TextBack,
MUIA_Text_Contents, "\33c Et un dernier avec \33uStringFrame\33n\n
(Escape pour quitter l'application)",
End,

Child, SimpleButton("Bouton sans action"),

End,
End,
End,
End;

Don't forget the extra "End,".

Intention is way important when writing such long MUI-macros or you'll soon loose track into which group which objects falls.