Go to URL to load XLST-based mandelbrot.xml. Notice WebKit's performance - particularly the spinning beach-ball, long load time, and lack of incremental rendering. The same page loads significantly faster under Google Chrome on Windows. Try it. It is also faster on Firefox Mac (but not as fast as Chrome). On IE Windows and Opera (Mac/Windows) it updates incrementally - which looks much better than a spinning beach-ball - and should be done on Safari if it's taking so long to render. Finally, the result rendered by Safari is incorrect. If you compare it to the results in Google Chrome and IE on Windows, you can see that the right line endings are all alines (so it's a rectangle). This is not the case under Safari. Finally, the colors do not match those shown in IE or Opera. But this may not be a bug, since Chrome and Firefox show similar colors to WebKit. Tested with WebKit nightly. Now load the same page with IE under windows.
WebKit won't get incremental rendering as the results are parser as a serialized string from libxslt. That interface between libxslt and WebKit is probably slowing this down because of the sheer number of 'span' elements generated that then need to be parsed and rendered. One way to speed this up is to make a tighter coupling between the output of the XSLT engine and the DOM load/render.