[metapost] label.rt(TEX("\tiny little label"), (0, 0)); does not work

[stefan knorr]

dear list,
i tried to typeset some smaller labels:
label.rt(TEX("\tiny little label"), (0, 0));     --- does not work
label.rt(btex \tiny little label etex, (0, 0));  --- works

how can i use standard latex commands like \small \tiny in the TEX() 
command. i like the TEX command, because it offers some advantages for 
string combination:
label.rt(TEX("label " & decimal(number) & " going on"), (0, 0));

regards,
stefan