Illustrator Scripting :: Select ALL Objects Directly Below Object?

Is there a way to simply select all object directly below an objects?
 
I found this script here but it doesn't seem to work.  
 
//DESCRIPTION:Select Below
// A Jongware Script
if (app.documents.length && app.selection.length)
{
ypos = app.selection[0].visibleBounds[3];

[Code] .....  

Here's an example file. I'm trying to select eveything below the yellow polygon.
 
This would be very useful in another project with many small objects bunch together below many larger objects. I want to group the small objects that are bellow the larger object together without having to manually select each objects (there are thousands of objects so a script would be ideal).