letters "a"--"z", digits, and the characters plus ("+"), period ("."), and hyphen ("-") are allowed. For the sake of resiliency, programs interpreting Fidonet URLs SHOULD treat upper case letters in scheme names as equivalent to the corresponding lower case letters (e.g., allow "AREA" scheme name as well as "area").
Only the first colon of the URL plays the role of delimiter between <scheme> and <scheme-specific-part>. The scheme-specific part of any URL MAY contain other colons.
The colon delimiter between <scheme> and <scheme-specific-part> MAY be immediately followed by an optional double slash ("//"). Fidonet programs interpreting URLs MUST treat the delimiter "://" as equivalent to the simple colon before <scheme-specific-part>.
5.1.1. Conformance note -+---------------------
This subsection is informative.
The Fidonet URL schemes defined in this document consist of lower case letters "a"--"z" only. However, digits, and the characters plus ("+"), period ("."), and hyphen ("-") MUST also be allowed in scheme names, so that Internet schemes conforming with the specifications of RFC 1738 are correctly dealt with.
In current Internet practice they distinguish between delimiters ":" and "://". The delimiter "://" is often used after scheme names that designate objects and resources ("http://", "ftp://", "gopher://", "nntp://", "ed2k://", "file://", etc.). The delimiter ":" is often used after scheme names that designate actions (e.g. "mailto:", "skype:").
The same difference exists between Fidonet resources (objects) and actions. That's why, though these delimiters MUST always be interpreted as equivalent, it is still RECOMMENDED that ":" SHOULD be used after schemes that designate actions ("netmail:", "echomail:", "areafix:") and "://" SHOULD be used after schemes that designate resources ("area://", "freq://", "fecho://", "faqserv://", etc.).
5.2. URL character encoding -+-------------------------
URLs are sequences of characters (i.e., letters, digits, and/or special characters). URLs may be represented in a variety of ways: e.g., ink on paper, or a sequence of octets in a coded character set. The interpretation of URL depends only on the identity of the characters used.
It is useful to distinguish between a "character" (distinguishable semantic entity) and an "octet" (an 8-bit byte).
In most URL schemes, the character sequences in different parts of a URL are used to represent sequences of octets used in Fidonet services. For example, in the "netmail:" scheme, the Fidonet address, netmail subject and addressee name are such sequences of octets, represented by parts of the URL. That sequences of octets, in turn, represent the original characters (of subject line, or of sysop's name, etc.); each original character is represented by one or more octets.
So there are always two mappings, one from URL characters to octets, and the second from octets to original characters:
URL character sequence<->octet sequence<->original character sequence
5.2.1. Encoding of original characters -+------------------------------------
The following paragraph is informative.
The sequence of octets defined by a component of the URL is subsequently used to represent a sequence of original characters. That process could have a very volatile nature. Being an international network, Fidonet always needs to deal with hundreds of national characters, with dozens of available encoding traditions and character sets. There is a number of FSC (Fidonet Standard Proposal documents) suggesting several kludge-based methods to define which character set is used. However, it is not wise to implement any equivalents to kludges as a required part of every Fidonet URL; and it could be hard to mantain complete lists of all possible character sets inside all programs interpreting Fidonet URLs. (Remember, it should be also made possible for Fidonet URLs to appear and be well interpreted in traditional HTML hypertext environment of the Web, Internet e-mail, instant messaging, etc.) That's why only one encoding, with large enough character set, has to be chosen.
The following paragraphs of this subsection are normative.
The sequence of octets used in Fidonet URLs MUST always contain UTF-8 encoded representation of original characters.
ISO/IEC 10646-1 defines a multi-octet character set called the Universal Character Set (UCS), which encompasses most of the world's writing systems. And UTF-8, one of a few so-called UCS transformation formats (UTF), preserves the 7-bit ASCII range, thus providing some compatibility with file systems, parsers and other software elements that rely on 7-bit ASCII values but are transparent to other values.
UTF-8 is defined in RFC 2279. Its description can also be found in Unicode Technical Report #4 and in the Unicode Standard, version 2.0.
5.2.2. Encoding of octets -+-----------------------
The character sequences in different parts of a URL are used to represent sequences of octets.
It is possible to represent an octet by the chararacter which has that octet as its code within the pure 7-bit ASCII character set. However, there are some exceptions (see below).
Alternatively, octets MAY be encoded by a character triplet consisting of the character "%" followed by the two hexadecimal digits (from "0123456789ABCDEF") which form the hexadecimal value of the octet. (The characters "abcdef" MAY also be used in hexadecimal encodings.)
Hexadecimal encoding of any octet MAY be used even when it is not REQUIRED or RECOMMENDED. However, it is RECOMMENDED to avoid unnecessary hexadecimal encoding, thus keeping URLs reasonably short.
It is either REQIRED or RECOMMENDED to use the hexadecimal encoding of octets if they have no corresponding graphic character within the 7-bit ASCII character set, or if the use of the corresponding character is unsafe, or if the corresponding character is reserved for some other interpretation within the particular URL scheme. These requirements and recommendations are detailed below.
5.2.2.1. No corresponding graphic 7-bit character -+-----------------------------------------------
URLs are written only with the graphic printable characters of the 7-bit ASCII coded character set.
The octets 80-FF hexadecimal do not belong to 7-bit ASCII, and the octets 00-1F and 7F hexadecimal represent control characters; these octets MUST be encoded.
--- Подошёл фидошник к киоску ,,Пиpожки``: дайте, пожалуйста, два-тpи сабжа... * Origin: Тогда советские ── по пояс в снегу ── двинулись вперёд! (2:5063/88)
