What happens when the execution time limit is exceeded?

It would seem that exceeding the execution time can be caught by declaring a handler with set_error_handler. However, even though I'm sure I've read something about it somewhere, I can't now find any info about what happens next. Specifically, inside my error handler, how long does the error handler then have to clean up? Can I do set_time_limit() again and return? (not that I'm minded to, but it might be useful to someone). I seem to have enough time to output some stuff back to the browser and log an error message or two, but it might be useful to know the actual limits. -- Cheers -- Tim