Spoiler Plugin - Support

[singulae]

I like it. Has great potential..

It would be much better if the button's appearance could change with CSS..

Some recommendations:
To avoid conflicts with other plugins that using window.load:

Code:

// unobtrusive way for call window.onload
  function addEvent(obj, evType, fn){
    if (obj.addEventListener){
      obj.addEventListener(evType, fn, false);
      return true;
    } else if (obj.attachEvent){
      var r = obj.attachEvent("on"+evType, fn);
      return r;
    } else {
      return false;
    }
  }
  
  addEvent(window, 'load', yourFunctionLaunchOnWindowLoad);

For check if exists the tag [spoiler] and avoid loading code that do not is used in other pages:

Code:

function check()
{
    global $data_index;    
    if (strpos($data_index->content, '[spoiler]') === false)
    {
        return false;
    }    
    add_action('theme-header','code');
}