it looks like we really need to use
<a href="foo.php?a=1&b=2">click me</a>
that is, the "&" instead of "&"
using "&" works in most cases except that some Facebook package will not take it as valid XHTML... so I am forced to use "&"
however, I am worried that using "&" may choke some browsers like IE 6 or even IE 5.5? Or does any one know that it is well supported by most browsers? Thanks.