It's an extremely poorly worded and unnecessary message. Really? You're going to make the message be
"WARNING: Custom scripts included on this page may cause unexpected behavior", which makes you think there is a completely different and larger problem, than just
"remember! you have js code!"?? Over the last 3000 hours of Splunk developing, I never once thought that the error message was just a simple "remember you have js code" reminder, and always thought there was some stability problem.
If you don't know how code works and the fact that code might call other code (wait really?), you should not be editing SimpleXML to begin with. At least word the message better.