Passing parameters between pages using query string parameters (
adding "&myarg=1" to the url) is handy in many situations.
In Umbraco XSLT this can easily be done using the
umbraco.library:RequestQueryString library
function.
umbraco.library:RequestQueryString('MediaRoot')
will return the value of the "?MediaRoot" argument.
See the Paging hint-page for an example.