XML tag & text field & eval()

See the .fla first pls. :))
I want to use this for a demo of XML , a tag finder application the element position is introduced in a textfield reprezented by viewedelement
The xmldocument.xml can be any .xml document

The problem: when I use as below not work, but if change childNodes[0]. with firstChild. it is OK. I suppose is a problem with the eval() function
what can do with? any suggestion ? Thanks