> <a href='../upper.html'> UPPER </a><br>
> <a href='../../upper.html'> UPPER </a><br>
> <a href='../../../upper.html'> UPPER </a><br>
> <a href='../../../../upper.html'> UPPER </a><br>

Actually, these links will work (they will be "restricted" - not linking above
"root domain"), but if you add a "/" at the start of the URL, then that is
when the problems occur:

<a href='/../../upper.html'> UPPER </a><br>