Dynamic Springboard icons?

[LoneWolf121188]

So I was thinking...the calendar icon on the Springboard is dynamic, ie, it changes depending on certain settings in the app (what the day and date are). How does this work, and more importantly, would it be possible to write apps that also do this? I was thinking specifically of the weather app: it would be great if the icon wasn't stuck at 73 degrees and sunny, but if it actually changed depending on the weather.