> 2.4.3. Excluded US-ASCII Characters > Although they are disallowed within the URI syntax, we include here a > description of those US-ASCII characters that have been excluded and > the reasons for their exclusion. (中略) > Other characters are excluded because gateways and other transport > agents are known to sometimes modify such characters, or they are > used as delimiters. > > unwise = "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`" > > Data corresponding to excluded characters must be escaped in order to > be properly represented within a URI.