Как вычислить разницу между двумя датами в днях?

li.collapsed > ul {display:block!important} #w_search_history div.collapsed div, #w_search_history div.collapsed ul {display:block!important} ul.tree li.collapsed {background-image:none !important} #w_metadata_toc li.collapsed, #w_search_history div.collapsed, #w_search_history li.collapsed {background-image:url('/img/its/tree/expanded.gif') !important} #l_toc a:active, #l_toc a:focus {background-color:#faefb5} #l_toc_inner, #l_nav_inner {overflow:auto;padding-right:0}

.noscript{display:inherit!important} .script{display:none!important} .w.loading > *,.l.loading > *{visibility:inherit} .w.loading,.l.loading{cursor:inherit;background:inherit;background-position:inherit} .l.loading{margin:inherit;padding:inherit} #other_sites_link {display:none} #contact {margin-top:12px}