According to RFC 4193, unique local addresses will always have a prefix of `FD00::/8`.. but according to Wikipedia:

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> The block fd00::/8 is defined for /48 prefixes, formed by setting the forty least-significant bits of the prefix to a randomly generated bit string.
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> 
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Is this enforced, and if so why? What stops me from having a prefix of `/32` or `/16` etc?