This section discusses limitations on characters and character sequences usable for IRIs beyond those given in section 2.2 and section 4.1. The considerations in this section are relevant when IRIs are created and when URIs are converted to IRIs.
この章では
a. The repertoire of characters allowed in each IRI component is limited by the definition of that component. For example, the definition of the scheme component does not allow characters beyond US-ASCII.
(Note: In accordance with URI practice, generic IRI software cannot and should not check for such limitations.)
(注意:
b. The UCS contains many areas of characters for which there are strong visual look-alikes. Because of the likelihood of transcription errors, these also should be avoided. This includes the full-width equivalents of Latin characters, half-width Katakana characters for Japanese, and many others. It also includes many look-alikes of "space", "delims", and "unwise", characters excluded in [RFC3491].
,
区切
, 賢くない
Additional information is available from [UNIXML]. [UNIXML] is written in the context of running text rather than in that of identifiers. Nevertheless, it discusses many of the categories of characters not appropriate for IRIs.
追加情報が
Although an IRI is defined as a sequence of characters, software interfaces for URIs typically function on sequences of octets or other kinds of code units. Thus, software interfaces and protocols MUST define which character encoding is used.
Intermediate software interfaces between IRI-capable components and URI-only components MUST map the IRIs per section 3.1, when transferring from IRI-capable to URI-only components. This mapping SHOULD be applied as late as possible. It SHOULD NOT be applied between components that are known to be able to handle IRIs.
Document formats that transport URIs may have to be upgraded to allow the transport of IRIs. In cases where the document as a whole has a native character encoding, IRIs MUST also be encoded in this character encoding and converted accordingly by a parser or interpreter. IRI characters not expressible in the native character encoding SHOULD be escaped by using the escaping conventions of the document format if such conventions are available. Alternatively, they MAY be percent-encoded according to section 3.1. For example, in HTML or XML, numeric character references SHOULD be used. If a document as a whole has a native character encoding and that character encoding is not UTF-8, then IRIs MUST NOT be placed into the document in the UTF-8 character encoding.
Note: Some formats already accommodate IRIs, although they use different terminology. HTML 4.0 [HTML4] defines the conversion from IRIs to URIs as error-avoiding behavior. XML 1.0 [XML1], XLink [XLink], XML Schema [XMLSchema], and specifications based upon them allow IRIs. Also, it is expected that all relevant new W3C formats and protocols will be required to handle IRIs [CharMod].
注意: 幾つかの書式は
This section discusses details and gives examples for point c) in section 1.2. To be able to use IRIs, the URI corresponding to the IRI in question has to encode original characters into octets by using UTF-8. This can be specified for all URIs of a URI scheme or can apply to individual URIs for schemes that do not specify how to encode original characters. It can apply to the whole URI, or only to some part. For background information on encoding characters into URIs, see also section 2.5 of [RFC3986].
この章は1.2節の c) についての詳細と例を示します。
For new URI schemes, using UTF-8 is recommended in [RFC2718]. Examples where UTF-8 is already used are the URN syntax [RFC2141], IMAP URLs [RFC2192], and POP URLs [RFC2384]. On the other hand, because the HTTP URL scheme does not specify how to encode original characters, only some HTTP URLs can have corresponding but different IRIs.
新しい
For example, for a document with a URI of "http://www.example.org/r%C3%A9sum%C3%A9.html", it is possible to construct a corresponding IRI (in XML notation, see, section 1.4): "http://www.example.org/résumé.html" ("é"; stands for the e-acute character, and "%C3%A9" is the UTF-8 encoded and percent-encoded representation of that character). On the other hand, for a document with a URI of "http://www.example.org/r%E9sum%E9.html", the percent-encoding octets cannot be converted to actual characters in an IRI, as the percent-encoding is not based on UTF-8.
例えば、 é は
This means that for most URI schemes, there is no need to upgrade their scheme definition in order for them to work with IRIs. The main case where upgrading makes sense is when a scheme definition, or a particular component of a scheme, is strictly limited to the use of US-ASCII characters with no provision to include non-ASCII characters/octets via percent-encoding, or if a scheme definition currently uses highly scheme-specific provisions for the encoding of non-ASCII characters. An example of this is the mailto: scheme [RFC2368].
これはほとんどの
This specification does not upgrade any scheme specifications in any way; this has to be done separately. Also, note that there is no such thing as an "IRI scheme"; all IRIs use URI schemes, and all URI schemes can be used with IRIs, even though in some cases only by using URIs directly as IRIs, without any conversion.
この仕様はどの scheme 仕様をも更新しません。更新は別途行われなければなりません。
また、IRI scheme
のようなものがないことにも注意して下さい。
すべての
URI schemes can impose restrictions on the syntax of scheme-specific URIs; i.e., URIs that are admissible under the generic URI syntax [RFC3986] may not be admissible due to narrower syntactic constraints imposed by a URI scheme specification. URI scheme definitions cannot broaden the syntactic restrictions of the generic URI syntax; otherwise, it would be possible to generate URIs that satisfied the scheme-specific syntactic constraints without satisfying the syntactic constraints of the generic URI syntax. However, additional syntactic constraints imposed by URI scheme specifications are applicable to IRI, as the corresponding URI resulting from the mapping defined in section 3.1 MUST be a valid URI under the syntactic restrictions of generic URI syntax and any narrower restrictions imposed by the corresponding URI scheme specification.
The requirement for the use of UTF-8 applies to all parts of a URI (with the potential exception of the ireg-name part; see section 3.1). However, it is possible that the capability of IRIs to represent a wide range of characters directly is used just in some parts of the IRI (or IRI reference). The other parts of the IRI may only contain US-ASCII characters, or they may not be based on UTF-8. They may be based on another character encoding, or they may directly encode raw binary data (see also [RFC2397]).
For example, it is possible to have a URI reference of "http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9", where the document name is encoded in iso-8859-1 based on server settings, but where the fragment identifier is encoded in UTF-8 according to [XPointer]. The IRI corresponding to the above URI would be (in XML notation) "http://www.example.org/r%E9sum%E9.xml#résumé";.
例えば、 http://www.example.org/r%E9sum%E9.xml#r%C3%A9sum%C3%A9
のように
Similar considerations apply to query parts. The functionality of IRIs (namely, to be able to include non-ASCII characters) can only be used if the query part is encoded in UTF-8.
同様のことが
Processing of relative IRI references against a base is handled straightforwardly; the algorithms of [RFC3986] can be applied directly, treating the characters additionally allowed in IRI references in the same way that unreserved characters are in URI references.