Why is a page starting with .. illegal?

I have a page called ..hi i get this error when visiting the page. Why is that illegal?

Server Error in '/' Application.
HTTP Error 400 - Bad Request.
V开发者_C百科ersion Information: ASP.NET Development Server 10.0.0.0 

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As part of the URI Specification (section 5.2, "relative resolution"), dots are always removed from the URI and used to specify relative paths. The double-dot .. refers to the parent path.

It's technically an invalid URI because these relative path tokens need to be followed by a path separator, i.e. the /. In your case, it's being followed by the text hi, which doesn't conform to the specification and comes back as a "bad request."

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".." denotes "parent directory" when referencing a file. "." denotes the current directory.

If you try to name it ..XXX, it assumes you're giving it a relative file path, and it looks in the parent directory.

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Are you talking about the file name ..? Well the problem with that is that .. refers to the parent directory which is a bad thing to access from a URL.

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Probably because .. is also the file name of the parent folder. The server is interpreting the request as the parent folder then hi.