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Zack Williamse940c7a2019-08-21 14:25:39 -07001// Copyright 2017 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package language implements BCP 47 language tags and related functionality.
6//
7// The most important function of package language is to match a list of
8// user-preferred languages to a list of supported languages.
9// It alleviates the developer of dealing with the complexity of this process
10// and provides the user with the best experience
11// (see https://blog.golang.org/matchlang).
12//
13//
14// Matching preferred against supported languages
15//
16// A Matcher for an application that supports English, Australian English,
17// Danish, and standard Mandarin can be created as follows:
18//
19// var matcher = language.NewMatcher([]language.Tag{
20// language.English, // The first language is used as fallback.
21// language.MustParse("en-AU"),
22// language.Danish,
23// language.Chinese,
24// })
25//
26// This list of supported languages is typically implied by the languages for
27// which there exists translations of the user interface.
28//
29// User-preferred languages usually come as a comma-separated list of BCP 47
30// language tags.
31// The MatchString finds best matches for such strings:
32//
33// handler(w http.ResponseWriter, r *http.Request) {
34// lang, _ := r.Cookie("lang")
35// accept := r.Header.Get("Accept-Language")
36// tag, _ := language.MatchStrings(matcher, lang.String(), accept)
37//
38// // tag should now be used for the initialization of any
39// // locale-specific service.
40// }
41//
42// The Matcher's Match method can be used to match Tags directly.
43//
44// Matchers are aware of the intricacies of equivalence between languages, such
45// as deprecated subtags, legacy tags, macro languages, mutual
46// intelligibility between scripts and languages, and transparently passing
47// BCP 47 user configuration.
48// For instance, it will know that a reader of Bokmål Danish can read Norwegian
49// and will know that Cantonese ("yue") is a good match for "zh-HK".
50//
51//
52// Using match results
53//
54// To guarantee a consistent user experience to the user it is important to
55// use the same language tag for the selection of any locale-specific services.
56// For example, it is utterly confusing to substitute spelled-out numbers
57// or dates in one language in text of another language.
58// More subtly confusing is using the wrong sorting order or casing
59// algorithm for a certain language.
60//
61// All the packages in x/text that provide locale-specific services
62// (e.g. collate, cases) should be initialized with the tag that was
63// obtained at the start of an interaction with the user.
64//
65// Note that Tag that is returned by Match and MatchString may differ from any
66// of the supported languages, as it may contain carried over settings from
67// the user tags.
68// This may be inconvenient when your application has some additional
69// locale-specific data for your supported languages.
70// Match and MatchString both return the index of the matched supported tag
71// to simplify associating such data with the matched tag.
72//
73//
74// Canonicalization
75//
76// If one uses the Matcher to compare languages one does not need to
77// worry about canonicalization.
78//
79// The meaning of a Tag varies per application. The language package
80// therefore delays canonicalization and preserves information as much
81// as possible. The Matcher, however, will always take into account that
82// two different tags may represent the same language.
83//
84// By default, only legacy and deprecated tags are converted into their
85// canonical equivalent. All other information is preserved. This approach makes
86// the confidence scores more accurate and allows matchers to distinguish
87// between variants that are otherwise lost.
88//
89// As a consequence, two tags that should be treated as identical according to
90// BCP 47 or CLDR, like "en-Latn" and "en", will be represented differently. The
91// Matcher handles such distinctions, though, and is aware of the
92// equivalence relations. The CanonType type can be used to alter the
93// canonicalization form.
94//
95// References
96//
97// BCP 47 - Tags for Identifying Languages http://tools.ietf.org/html/bcp47
98//
99package language // import "golang.org/x/text/language"
100
101// TODO: explanation on how to match languages for your own locale-specific
102// service.