Well... But URLs ARE case sensetive. Not the domane names, but "path" part is not imply any case-isensitivity rule, and most servers by default will distinguish some.domain/Some/Path and some.domain/some/path
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Moreover, if we speak about an abstract url schema://host/path besides http, as an identifier (without implicit domain name resolution process) even the host part may be processed in casse-sensetive way
I faced the case sensitivities for domain names in some implementation of xml schema directory ten+ years ago. Even now I'm unsure if threre is explicit requirements to treat it as c-isensetive