How To Pass Values To A Function In Form

In the DOM Scripting book by Jeremy Keith, he provides this function:
Code:
function styleElementSiblings(tag,theclass) {
if (!document.getElementsByTagName) return false;
var elems = document.getElementsByTagName(tag);
for (var i=0; i<elems.length; i++) {
var elem = getNextElement(elems[i].nextSibling);
addClass(elem,theclass);
} }

And then says to pass the values "h1" and "intro" to this function in this form:
styleElementSiblings("h1","intro");

I'm just a little stuck on how to "pass the values". Presumably I've missed something simple. I've tried just pasting that line before the function, but no luck. He also provides a function that allows multiple functions to load at once, called addLoadEvent, so I tried this, also with no luck:
addLoadEvent(styleElementSiblings("h1","intro"));