2.2. Reserved Characters
URIs include components and subcomponents that are delimited by
characters in the "reserved" set. These characters are called
"reserved" because they may (or may not) be defined as delimiters by
the generic syntax, by each scheme-specific syntax, or by the
implementation-specific syntax of a URI's dereferencing algorithm.
If data for a URI component would conflict with a reserved
character's purpose as a delimiter, then the conflicting data must be
percent-encoded before the URI is formed.
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
Vagyis az URI-ben olyan komponenst keresünk, ami sub-delims-t tartalmazhat és szintaktikailag állhat azon a helyen, ahol a Wikipedia URI-ben.
Appendix A. Collected ABNF for URI
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
hier-part = "//" authority path-abempty
/ path-absolute
/ path-rootless
/ path-empty
authority = [ userinfo "@" ] host [ ":" port ]
userinfo = *( unreserved / pct-encoded / sub-delims / ":" )
path-abempty = *( "/" segment )
path-absolute = "/" [ segment-nz *( "/" segment ) ]
path-rootless = segment-nz *( "/" segment )
path-empty = 0<pchar>
segment = *pchar
segment-nz = 1*pchar
A scheme, query és fragment part nem érintett, marad a hier-part. Az authority-ben ugyan lehetne sub-delim, de szintaktikailag annak az első / előtt kell állnia. A többi lehetséges komponensben nem szerepel sub-delim. Vagyis a http://hu.wikipedia.org/wiki/M%C3%A1trix_(matematika) URI valid a zárójelek encode-olása nélkül is.
2.2. URL Character Encoding Issues
...
Thus, only alphanumerics, the special characters "$-_.+!*'(),", and
reserved characters used for their reserved purposes may be used
unencoded within a URL.