A variant, where the format string itself is long, does not work in either compiled or uncompiled modes.

```
% set s [testbigdata string 0x100000000] ; string length $s
4294967296
% append s %s ; string length $s
4294967298
% string length [format $s X]
max size for a Tcl value exceeded
% string length [$format $s X]
max size for a Tcl value exceeded
```

Further, large values for precision and width raise the same error.