Call to undefined (helper) function

Thanks for the suggestions InsiteFX, and the info that helpers are in the App namespace (which seems sensible, but I'd not thought of).

I have been messing around with some (seemingly unrelated) image-processing stuff, and a bit of CSRF experimentation (which may be more likely the cause (?))...

As an initial experiment, I did try to add a path to my view insertion: <?=\App\myhelperFunction();?>

This results in: Error: Call to undefined function App\myhelperFunction()