Nothing in general actually.
EXSLT is a community initiative to provide extensions to XSLT, and currently it defines more than 70 extension functions and elements. EXSLT provides benefits to the average XML developer in two different ways—first of all, it provides an extremely rich library of commonly needed functionality that is lacking in XSLT 1.0, and secondly it makes XSLT stylesheets more portable, at least between XSLT processors supporting EXSLT.