Recover instance from a reference

Hi,
I found on Autodesk forum a line of script to recover the instance from a reference object.

I mean :
- I create an Object A
- I copy it as a reference ( B) , I apply a modifier on it
- I select B and apply the script, I get an instance of A.

The line of script is : Line baseObject:$.baseObject

I don't find any explanation, why "line" ?

And it works on some files, but in a heavy file I work it don't work, ans use another object...

Anybody have any idea ? Or an another solution ?
Thanks.