documentclass{article}

defhide#1#2{%
setbox1vbox{}%
gdeftxt{#1}%
setbox0vbox{hsize5cm raggedright
#2%
par
loop
unpenalty
skip0lastskipunskipglobalsetbox1vbox{vskipskip0unvbox1}%
unpenalty
skip0lastskipunskipglobalsetbox1vbox{vskipskip0unvbox1}%
unpenalty
setbox0lastbox
ifvoid0
else
globalsetbox1vbox{%
dimen0dp0
count0=96
expandaftergetnexttxt{}relax
dimen2dimexprcount0 sp - 109sprelax
kern10000dimen2
box0
kern-10000dimen2
kern-dimen0
hrule
kerndimen0
unvbox1}%
repeat
}
leavevmodebox1
}

defgetnext#1#2relax{%
ifx\#1\%
gdeftxt{}%
else
ifx #1%
count0=95
else
count0=`#1
fi
gdeftxt{#2}%
fi}




begin{document}
Large

hide{hello}{
defa{One two three four five six seven eight nine ten. }
defb{a Red yellow blue green. aa One two three. }
bb}
hide{david}{
defa{One two three four five six seven eight nine ten. }
defb{a Red yellow blue green. aa One two three. }
bb}



end{document}