You would just have to concatenate everything and add an indent parameter, something like the code below.
function test()
{
alert(traverseElements(startElement, ''));
}
function traverseElements(elem, indent)
{
var result = indent + elem.innerHTML + '\n';
for (i=0; i<elem.elements.length; i++)
{
result += indent + traverseElements(elem.elements(i), indent + ' ');
}
return result;
}
Good luck!