* The main focus point is _not_ performance. This is a simple layout library, guys, not [compiz](https://www.google.com/search?q=compiz&tbm=isch) piped into [libcaca](https://www.google.com/search?q=libcaca&tbm=isch). Unless you are running it on your microwave's microcontroller, it's not going to be slow.
* The library is single-threaded. Thus, callback methods are blocking - careful what you're doing in there! Feel free to use threads on your side, though.