What dose this lines of js code means:

```
        ('selectionchange',function(sm, rs) {
            if (rs.length) {
                var detailPanel = Ext.getCmp('detailPanel');
                bookTpl.overwrite(detailPanel.body, rs[0].data);
            }
        })

```

this is a part of below link:
<http://dev.sencha.com/deploy/ext-4.0.2a/examples/grid/binding-with-classes.js>

---

Update:
I removed these lines and code runs without any diffrenece!
It's a coding mistake
Thanks all