At 14:18 30.05.00 -0700, you wrote:
>         str first: (3 min: str size).


Hm, I created a change including Dave's suggestion with strict error 
checking but then, I thought that

         first: n

might be ambiguous, as it could also be a shortcut for

         at: 1 put: n

so perhaps

         copyFirst: n

might be a better name which also matches copyAfter: (new), copyAfterLast:, 
copyUpTo: and copyUpToLast:.

Yes/No/Maybe?
--
Stefan Matthias Aust \\ Truth Until Paradox