I have a page with a link and a DIV with visibility=hidden. The target of the link is to a hidden IFRAME. The link executes a script in the hidden IFRAME. When the user clicks the link, I change the DIV's visibility to visible. Depending on a condition in the script executing in the hidden IFRAME, I want to change the DIV's visibility back to hidden. How would I do this?

I tried
document.parentWindow.all("DIV").style.visibility = "hidden"
but it didn't work.