Expander plugin: There's an expandEffect, why no collapseEffect?

Expander plugin: There's an expandEffect, why no collapseEffect?

I'm using the expander plugin with little problems, and I'm using the "slideDown" effect for my "expandEffect" parameter to display my panel, but I'd like to see it "slideUp" when the user collapses the panel. Instead, the panel just vanishes.

So my question is, why is there no collapseEffect?