> it has nothing to do with requiring a function to be set. the problem > is that the function is free to change its mind at any moment, but we > rely on it returning the same value during some fixed periods of time. > if we truly want to support isvisible() we would need to cache/memoize > the value for the period we assume it to be constant.
Yes, that's what I'm saying. > but, defining > these caching regions is very difficult, and maintaining them as we > work on core we be even more difficult still. I don't think it would be that difficult, but certainly not something worth doing at this stage. Eelco
