It should be well known that a internet URL can point to either a folder or a file.
A folder usually responds with a default page -- e.g. index.html.
A file responds with itself.
In either case, you don't know which one you are getting. Imagine for instance ("http://www.example.com/fileorfolder.html"). Is it an oddly named folder that is returning a default file or is it a file?
How do I tell?