How to modify text in text Layer?

Hi All,

i'm trying to modify text in text layer:

var txtLayer=app.project.item(1).layer(1).property("Text").property("Source Text");

txtLayer.Setvalue("new text");

when i run the script it display the error: "function txtLayer.SetValue is undefined".

can someone help me to understand what i did wrong?

thanks in advance,

Guy