Which is to say that src="/..." refers to the root of your app package (the /) and you can do relative references from there. If for some reason you've loaded an HTML page that's in a subfolder of the app package, then ../ can be used to refer to something
in the package root, but then you might as well just prefix it with / to begin with.
As Jeff suggests, trying to get to the parent folder of the app package isn't allowed.
If you have a particular scenario in mind we might be able to be more specific.
.Kraig