This spoiler tag is like the others, for a more in-depth explanation go to one of those. I just quickly modded it because it was requested by Andrew.
Basically, this code is much like V2- in V2, the user would type in
[spoiler=Hello]Secret[/spoiler]
and it would show the text "Hello" as a link, and when clicked would reveal the text "Secret".
In V3, the code above ([spoiler=Hello]Secret[/spoiler]) would show the text "(show)" as a link, and under it would be "Hello" in italics, when (show) was clicked on it would reveal "Secret".
I hope you get where I'm going with this;
Preview is here.<script>
var b = document.getElementsByTagName("div");
//Created by Agent Moose (smcodes.smfforfree3.com)
for(x=0;x<b.length;x++){
if(b[x].className=="post" && b[x].innerHTML.match(/\[spoiler=(.*)\](.*)\[\/spoiler\]/i)){
b[x].innerHTML = b[x].innerHTML.replace("[spoiler=" + RegExp.$1 + "]" + RegExp.$2 + "[/spoiler]","<div><div><a href='javascript:void(0)' onclick='$(this).parent().next().toggle()'>(show)<br /></a><i>" + RegExp.$1 + "</i></div><div style='display:none' id='spoiler'>" + RegExp.$2 + "</div></div>");
};};
</script>