If you are using prototype.js + effects.js or mootools.js, You can apply some effects anywhere on blog and there is various way to apply them. This is one of them and using javascript functions in Ajax-Spoiler plugin.

This post follows Ajax-Spoiler v0.9

There is some way to apply effects and this post explains one of them.
Check this post also.

1. Base

• All examples on this post will use ‘Spoiler.Collapse’ effect.
• Here is a simple example. (Click!)
  It’s done. Click again to hide me
• Code for above example is like this:

  Click!)
  It's done. Click again to hide me

• Spoiler.Collapse('id','effect',this) is the point.
• Element which ‘id’ is ‘mycont’ will be displayed and hid after click again.
• You can use all effects in Ajax-Spoiler plugin.

2. Apply

• Let’s apply it to sidebar.
• General sidebar.php template composed like this(default theme):

  
   
  
  .......sidebar menu....
   
  Categories
  
       
  
        
       
   
  
  ....and so on......