https://datatracker.ietf.org/doc/html/rfc3986#section-2.2
[[RFC3986]]より抜粋。
```
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
sub-delims = "!" / "
quot; / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
```