java script problem

![ex](http://dc110.4shared.com/img/4XofohdR/s7/0.2780194927130575/fgdf.JPG
)

in this script what is the duty of "documentgetelimentbyid"? what it does?
java script problem
===


![ex](http://dc110.4shared.com/img/4XofohdR/s7/0.2780194927130575/fgdf.JPG
)

in this script what is the duty of "documentgetelimentbyid"? what it does?