Volatile Tokenscript attribute

While designing the cryptokitties tokenscript we realised that a 'volatile' function attribute is required.

For example, there may be a function call to determine if a kitty is ready to give birth. The result of this call is dependent on block time since kitty was bred. Since there is no event published between the result being false and the result bring true, the function return should never be cached since there's no event or transaction update that heralds a value change.

Taken in, thanks loads!