Saxon is at the moment the only XSLT processor providing an implementation of version 2.0 of the specification. Saxon is written in Java and thus should be a bit slower than libxslt. But XSLT 2.0 brings a lot of new features that developers may enjoy : regular expressions, grouping, user-defined functions, etc.

Saxon may be a bit slower on the first call, but, because the result of the XSL transformation is saved in a cache on server side, the following calls should be a lot faster (If you are in mode cache=true, which is the default mode for a normal visitor).

If you wish to use it, add the following line
$GLOBALS['use_saxon']=true;
in the file Kernel/common/config.inc.php