variants and customization options.
</para>
</sect2>
+ <sect2 id="icu-locales">
+ <title>ICU Locales</title>
+ <sect3 id="icu-locale-names">
+ <title>ICU Locale Names</title>
+ <para>
+ The ICU format for the locale name is a <link
+ linkend="icu-language-tag">Language Tag</link>.
+
+<programlisting>
+CREATE COLLATION mycollation1 (PROVIDER = icu, LOCALE = 'ja-JP');
+CREATE COLLATION mycollation2 (PROVIDER = icu, LOCALE = 'fr');
+</programlisting>
+ </para>
+ </sect3>
+ <sect3 id="icu-canonicalization">
+ <title>Locale Canonicalization and Validation</title>
+ <para>
+ When defining a new ICU collation object or database with ICU as the
+ provider, the given locale name is transformed ("canonicalized") into a
+ language tag if not already in that form. For instance,
+
+<screen>
+CREATE COLLATION mycollation3 (PROVIDER = icu, LOCALE = 'en-US-u-kn-true');
+NOTICE: using standard form "en-US-u-kn" for locale "en-US-u-kn-true"
+CREATE COLLATION mycollation4 (PROVIDER = icu, LOCALE = 'de_DE.utf8');
+NOTICE: using standard form "de-DE" for locale "de_DE.utf8"
+</screen>
+
+ If you see this notice, ensure that the <symbol>PROVIDER</symbol> and
+ <symbol>LOCALE</symbol> are the expected result. For consistent results
+ when using the ICU provider, specify the canonical <link
+ linkend="icu-language-tag">language tag</link> instead of relying on the
+ transformation.
+ </para>
+ <para>
+ A locale with no language name, or the special language name
+ <literal>root</literal>, is transformed to have the language
+ <literal>und</literal> ("undefined").
+ </para>
+ <para>
+ ICU can transform most libc locale names, as well as some other formats,
+ into language tags for easier transition to ICU. If a libc locale name is
+ used in ICU, it may not have precisely the same behavior as in libc.
+ </para>
+ <para>
+ If there is a problem interpreting the locale name, or if the locale name
+ represents a language or region that ICU does not recognize, you will see
+ the following warning:
+
+<screen>
+CREATE COLLATION nonsense (PROVIDER = icu, LOCALE = 'nonsense');
+WARNING: ICU locale "nonsense" has unknown language "nonsense"
+HINT: To disable ICU locale validation, set parameter icu_validation_level to DISABLED.
+CREATE COLLATION
+</screen>
+
+ <xref linkend="guc-icu-validation-level"/> controls how the message is
+ reported. Unless set to <literal>ERROR</literal>, the collation will
+ still be created, but the behavior may not be what the user intended.
+ </para>
+ </sect3>
+ <sect3 id="icu-language-tag">
+ <title>Language Tag</title>
+ <para>
+ A language tag, defined in BCP 47, is a standardized identifier used to
+ identify languages, regions, and other information about a locale.
+ </para>
+ <para>
+ Basic language tags are simply
+ <replaceable>language</replaceable><literal>-</literal><replaceable>region</replaceable>;
+ or even just <replaceable>language</replaceable>. The
+ <replaceable>language</replaceable> is a language code
+ (e.g. <literal>fr</literal> for French), and
+ <replaceable>region</replaceable> is a region code
+ (e.g. <literal>CA</literal> for Canada). Examples:
+ <literal>ja-JP</literal>, <literal>de</literal>, or
+ <literal>fr-CA</literal>.
+ </para>
+ <para>
+ Collation settings may be included in the language tag to customize
+ collation behavior. ICU allows extensive customization, such as
+ sensitivity (or insensitivity) to accents, case, and punctuation;
+ treatment of digits within text; and many other options to satisfy a
+ variety of uses.
+ </para>
+ <para>
+ To include this additional collation information in a language tag,
+ append <literal>-u</literal>, which indicates there are additional
+ collation settings, followed by one or more
+ <literal>-</literal><replaceable>key</replaceable><literal>-</literal><replaceable>value</replaceable>
+ pairs. The <replaceable>key</replaceable> is the key for a <link
+ linkend="icu-collation-settings">collation setting</link> and
+ <replaceable>value</replaceable> is a valid value for that setting. For
+ boolean settings, the <literal>-</literal><replaceable>key</replaceable>
+ may be specified without a corresponding
+ <literal>-</literal><replaceable>value</replaceable>, which implies a
+ value of <literal>true</literal>.
+ </para>
+ <para>
+ For example, the language tag <literal>en-US-u-kn-ks-level2</literal>
+ means the locale with the English language in the US region, with
+ collation settings <literal>kn</literal> set to <literal>true</literal>
+ and <literal>ks</literal> set to <literal>level2</literal>. Those
+ settings mean the collation will be case-insensitive and treat a sequence
+ of digits as a single number:
+<screen>
+CREATE COLLATION mycollation5 (PROVIDER = icu, DETERMINISTIC = false, LOCALE = 'en-US-u-kn-ks-level2');
+SELECT 'aB' = 'Ab' COLLATE mycollation5 as result;
+ result
+--------
+ t
+(1 row)
+
+SELECT 'N-45' < 'N-123' COLLATE mycollation5 as result;
+ result
+--------
+ t
+(1 row)
+</screen>
+ </para>
+ <para>
+ See <xref linkend="icu-custom-collations"/> for details and additional
+ examples of using language tags with custom collation information for the
+ locale.
+ </para>
+ </sect3>
+ </sect2>
<sect2 id="locale-problems">
<title>Problems</title>
code byte values.
</para>
+ <note>
+ <para>
+ The <literal>C</literal> and <literal>POSIX</literal> locales may behave
+ differently depending on the database encoding.
+ </para>
+ </note>
+
<para>
Additionally, two SQL standard collation names are available:
<sect4 id="collation-managing-create-icu">
<title>ICU Collations</title>
- <para>
- ICU allows collations to be customized beyond the basic language+country
- set that is preloaded by <command>initdb</command>. Users are encouraged
- to define their own collation objects that make use of these facilities to
- suit the sorting behavior to their requirements.
- See <ulink url="https://unicode-org.github.io/icu/userguide/locale/"></ulink>
- and <ulink url="https://unicode-org.github.io/icu/userguide/collation/api.html"></ulink> for
- information on ICU locale naming. The set of acceptable names and
- attributes depends on the particular ICU version.
- </para>
-
- <para>
- Here are some examples:
-
- <variablelist>
- <varlistentry id="collation-managing-create-icu-de-u-co-phonebk-x-icu">
- <term><literal>CREATE COLLATION "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de-u-co-phonebk');</literal></term>
- <term><literal>CREATE COLLATION "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de@collation=phonebook');</literal></term>
- <listitem>
- <para>German collation with phone book collation type</para>
- <para>
- The first example selects the ICU locale using a <quote>language
- tag</quote> per BCP 47. The second example uses the traditional
- ICU-specific locale syntax. The first style is preferred going
- forward, and is used internally to store locales.
- </para>
- <para>
- Note that you can name the collation objects in the SQL environment
- anything you want. In this example, we follow the naming style that
- the predefined collations use, which in turn also follow BCP 47, but
- that is not required for user-defined collations.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry id="collation-managing-create-icu-und-u-co-emoji-x-icu">
- <term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = 'und-u-co-emoji');</literal></term>
- <term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = '@collation=emoji');</literal></term>
- <listitem>
- <para>
- Root collation with Emoji collation type, per Unicode Technical Standard #51
- </para>
- <para>
- Observe how in the traditional ICU locale naming system, the root
- locale is selected by an empty string.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry id="collation-managing-create-icu-en-u-kr-grek-latn">
- <term><literal>CREATE COLLATION latinlast (provider = icu, locale = 'en-u-kr-grek-latn');</literal></term>
- <term><literal>CREATE COLLATION latinlast (provider = icu, locale = 'en@colReorder=grek-latn');</literal></term>
- <listitem>
- <para>
- Sort Greek letters before Latin ones. (The default is Latin before Greek.)
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry id="collation-managing-create-icu-en-u-kf-upper">
- <term><literal>CREATE COLLATION upperfirst (provider = icu, locale = 'en-u-kf-upper');</literal></term>
- <term><literal>CREATE COLLATION upperfirst (provider = icu, locale = 'en@colCaseFirst=upper');</literal></term>
- <listitem>
- <para>
- Sort upper-case letters before lower-case letters. (The default is
- lower-case letters first.)
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry id="collation-managing-create-icu-en-u-kf-upper-kr-grek-latn">
- <term><literal>CREATE COLLATION special (provider = icu, locale = 'en-u-kf-upper-kr-grek-latn');</literal></term>
- <term><literal>CREATE COLLATION special (provider = icu, locale = 'en@colCaseFirst=upper;colReorder=grek-latn');</literal></term>
- <listitem>
- <para>
- Combines both of the above options.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry id="collation-managing-create-icu-en-u-kn-true">
- <term><literal>CREATE COLLATION numeric (provider = icu, locale = 'en-u-kn-true');</literal></term>
- <term><literal>CREATE COLLATION numeric (provider = icu, locale = 'en@colNumeric=yes');</literal></term>
- <listitem>
- <para>
- Numeric ordering, sorts sequences of digits by their numeric value,
- for example: <literal>A-21</literal> < <literal>A-123</literal>
- (also known as natural sort).
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
-
- See <ulink url="https://www.unicode.org/reports/tr35/tr35-collation.html">Unicode
- Technical Standard #35</ulink>
- and <ulink url="https://tools.ietf.org/html/bcp47">BCP 47</ulink> for
- details. The list of possible collation types (<literal>co</literal>
- subtag) can be found in
- the <ulink url="https://github.com/unicode-org/cldr/blob/master/common/bcp47/collation.xml">CLDR
- repository</ulink>.
- </para>
+ <para>
+ ICU collations can be created like:
- <para>
- Note that while this system allows creating collations that <quote>ignore
- case</quote> or <quote>ignore accents</quote> or similar (using the
- <literal>ks</literal> key), in order for such collations to act in a
- truly case- or accent-insensitive manner, they also need to be declared as not
- <firstterm>deterministic</firstterm> in <command>CREATE COLLATION</command>;
- see <xref linkend="collation-nondeterministic"/>.
- Otherwise, any strings that compare equal according to the collation but
- are not byte-wise equal will be sorted according to their byte values.
- </para>
+<programlisting>
+CREATE COLLATION german (provider = icu, locale = 'de-DE');
+</programlisting>
- <note>
+ ICU locales are specified as a BCP 47 <link
+ linkend="icu-language-tag">Language Tag</link>, but can also accept most
+ libc-style locale names. If possible, libc-style locale names are
+ transformed into language tags.
+ </para>
<para>
- By design, ICU will accept almost any string as a locale name and match
- it to the closest locale it can provide, using the fallback procedure
- described in its documentation. Thus, there will be no direct feedback
- if a collation specification is composed using features that the given
- ICU installation does not actually support. It is therefore recommended
- to create application-level test cases to check that the collation
- definitions satisfy one's requirements.
+ New ICU collations can customize collation behavior extensively by
+ including collation attributes in the langugage tag. See <xref
+ linkend="icu-custom-collations"/> for details and examples.
</para>
- </note>
</sect4>
-
<sect4 id="collation-copy">
<title>Copying Collations</title>
</tip>
</sect3>
</sect2>
+ <sect2 id="icu-custom-collations">
+ <title>ICU Custom Collations</title>
+
+ <para>
+ ICU allows extensive control over collation behavior by defining new
+ collations with collation settings as a part of the language tag. These
+ settings can modify the collation order to suit a variety of needs. For
+ instance:
+
+<programlisting>
+-- ignore differences in accents and case
+CREATE COLLATION ignore_accent_case (PROVIDER = icu, DETERMINISTIC = false, LOCALE = 'und-u-ks-level1');
+SELECT 'Å' = 'A' COLLATE ignore_accent_case; -- true
+SELECT 'z' = 'Z' COLLATE ignore_accent_case; -- true
+
+-- upper case letters sort before lower case.
+CREATE COLLATION upper_first (PROVIDER=icu, LOCALE = 'und-u-kf-upper');
+SELECT 'B' < 'b' COLLATE upper_first; -- true
+
+-- treat digits numerically and ignore punctuation
+CREATE COLLATION num_ignore_punct (PROVIDER = icu, DETERMINISTIC = false, LOCALE = 'und-u-ka-shifted-kn');
+SELECT 'id-45' < 'id-123' COLLATE num_ignore_punct; -- true
+SELECT 'w;x*y-z' = 'wxyz' COLLATE num_ignore_punct; -- true
+</programlisting>
+
+ Many of the available options are described in <xref
+ linkend="icu-collation-settings"/>, or see <xref
+ linkend="icu-external-references"/> for more details.
+ </para>
+ <sect3 id="icu-collation-comparison-levels">
+ <title>ICU Comparison Levels</title>
+ <para>
+ Comparison of two strings (collation) in ICU is determined by a
+ multi-level process, where textual features are grouped into
+ "levels". Treatment of each level is controlled by the <link
+ linkend="icu-collation-settings-table">collation settings</link>. Higher
+ levels correspond to finer textual features.
+ </para>
+ <para>
+ <table id="icu-collation-levels">
+ <title>ICU Collation Levels</title>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Level</entry>
+ <entry>Description</entry>
+ <entry><literal>'f' = 'f'</literal></entry>
+ <entry><literal>'ab' = U&'a\2063b'</literal></entry>
+ <entry><literal>'x-y' = 'x_y'</literal></entry>
+ <entry><literal>'g' = 'G'</literal></entry>
+ <entry><literal>'n' = 'ñ'</literal></entry>
+ <entry><literal>'y' = 'z'</literal></entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>level1</entry>
+ <entry>Base Character</entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>false</literal></entry>
+ </row>
+ <row>
+ <entry>level2</entry>
+ <entry>Accents</entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ </row>
+ <row>
+ <entry>level3</entry>
+ <entry>Case/Variants</entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ </row>
+ <row>
+ <entry>level4</entry>
+ <entry>Punctuation</entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ </row>
+ <row>
+ <entry>identic</entry>
+ <entry>All</entry>
+ <entry><literal>true</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ The above table shows which textual feature differences are
+ considered significant when determining equality at the given level. The
+ unicode character <literal>U+2063</literal> is an invisible separator,
+ and as seen in the table, is ignored for at all levels of comparison less
+ than <literal>identic</literal>.
+ </para>
+ <para>
+ At every level, even with full normalization off, basic normalization is
+ performed. For example, <literal>'á'</literal> may be composed of the
+ code points <literal>U&'\0061\0301'</literal> or the single code
+ point <literal>U&'\00E1'</literal>, and those sequences will be
+ considered equal even at the <literal>identic</literal> level. To treat
+ any difference in code point representation as distinct, use a collation
+ created with <symbol>DETERMINISTIC</symbol> set to
+ <literal>true</literal>.
+ </para>
+ <sect4 id="icu-collation-level-examples">
+ <title>Collation Level Examples</title>
+ <para>
+
+<programlisting>
+CREATE COLLATION level3 (PROVIDER=icu, DETERMINISTIC=false, LOCALE='und-u-ka-shifted-ks-level3');
+CREATE COLLATION level4 (PROVIDER=icu, DETERMINISTIC=false, LOCALE='und-u-ka-shifted-ks-level4');
+CREATE COLLATION identic (PROVIDER=icu, DETERMINISTIC=false, LOCALE='und-u-ka-shifted-ks-identic');
+
+-- invisible separator ignored at all levels except identic
+SELECT 'ab' = U&'a\2063b' COLLATE level4; -- true
+SELECT 'ab' = U&'a\2063b' COLLATE identic; -- false
+
+-- punctuation ignored at level3 but not at level 4
+SELECT 'x-y' = 'x_y' COLLATE level3; -- true
+SELECT 'x-y' = 'x_y' COLLATE level4; -- false
+</programlisting>
+
+ </para>
+ </sect4>
+ </sect3>
+ <sect3 id="icu-collation-settings">
+ <title>Collation Settings for an ICU Locale</title>
+ <para>
+ <table id="icu-collation-settings-table">
+ <title>ICU Collation Settings</title>
+ <tgroup cols="4">
+ <thead>
+ <row>
+ <entry>Key</entry>
+ <entry>Values</entry>
+ <entry>Default</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>ks</literal></entry>
+ <entry><literal>level1</literal>, <literal>level2</literal>, <literal>level3</literal>, <literal>level4</literal>, <literal>identic</literal></entry>
+ <entry><literal>level3</literal></entry>
+ <entry>
+ Sensitivity (or "strength") when determining equality, with
+ <literal>level1</literal> the least sensitive to differences and
+ <literal>identic</literal> the most sensitive to differences. See
+ <xref linkend="icu-collation-levels"/> for details.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>ka</literal></entry>
+ <entry><literal>noignore</literal>, <literal>shifted</literal></entry>
+ <entry><literal>noignore</literal></entry>
+ <entry>
+ If set to <literal>shifted</literal>, causes some characters
+ (e.g. punctuation or space) to be ignored in comparison. Key
+ <literal>ks</literal> must be set to <literal>level3</literal> or
+ lower to take effect. Set key <literal>kv</literal> to control which
+ character classes are ignored.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kb</literal></entry>
+ <entry><literal>true</literal>, <literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry>
+ Backwards comparison for the level 2 differences. For example,
+ locale <literal>und-u-kb</literal> sorts <literal>'àe'</literal>
+ before <literal>'aé'</literal>.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kk</literal></entry>
+ <entry><literal>true</literal>, <literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry>
+ <para>
+ Enable full normalization; may affect performance. Basic
+ normalization is performed even when set to
+ <literal>false</literal>. Locales for languages that require full
+ normalization typically enable it by default.
+ </para>
+ <para>
+ Full normalization is important in some cases, such as when
+ multiple accents are applied to a single character. For instance,
+ <literal>'ệ'</literal> can be composed of code points
+ <literal>U&'\0065\0323\0302'</literal> or
+ <literal>U&'\0065\0302\0323'</literal>. With full normalization
+ on, these code point sequences are treated as equal; otherwise they
+ are unequal.
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kc</literal></entry>
+ <entry><literal>true</literal>, <literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry>
+ <para>
+ Separates case into a "level 2.5" that falls between accents and
+ other level 3 features.
+ </para>
+ <para>
+ If set to <literal>true</literal> and <literal>ks</literal> is set
+ to <literal>level1</literal>, will ignore accents but take case
+ into account.
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kf</literal></entry>
+ <entry>
+ <literal>upper</literal>, <literal>lower</literal>,
+ <literal>false</literal>
+ </entry>
+ <entry><literal>false</literal></entry>
+ <entry>
+ If set to <literal>upper</literal>, upper case sorts before lower
+ case. If set to <literal>lower</literal>, lower case sorts before
+ upper case. If set to <literal>false</literal>, the sort depends on
+ the rules of the locale.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kn</literal></entry>
+ <entry><literal>true</literal>, <literal>false</literal></entry>
+ <entry><literal>false</literal></entry>
+ <entry>
+ If set to <literal>true</literal>, numbers within a string are
+ treated as a single numeric value rather than a sequence of
+ digits. For example, <literal>'id-45'</literal> sorts before
+ <literal>'id-123'</literal>.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kr</literal></entry>
+ <entry>
+ <literal>space</literal>, <literal>punct</literal>,
+ <literal>symbol</literal>, <literal>currency</literal>,
+ <literal>digit</literal>, <replaceable>script-id</replaceable>
+ </entry>
+ <entry></entry>
+ <entry>
+ <para>
+ Set to one or more of the valid values, or any BCP 47
+ <replaceable>script-id</replaceable>, e.g. <literal>latn</literal>
+ ("Latin") or <literal>grek</literal> ("Greek"). Multiple values are
+ separated by "<literal>-</literal>".
+ </para>
+ <para>
+ Redefines the ordering of classes of characters; those characters
+ belonging to a class earlier in the list sort before characters
+ belonging to a class later in the list. For instance, the value
+ <literal>digit-currency-space</literal> (as part of a language tag
+ like <literal>und-u-kr-digit-currency-space</literal>) sorts
+ punctuation before digits and spaces.
+ </para>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>kv</literal></entry>
+ <entry>
+ <literal>space</literal>, <literal>punct</literal>,
+ <literal>symbol</literal>, <literal>currency</literal>
+ </entry>
+ <entry><literal>punct</literal></entry>
+ <entry>
+ Classes of characters ignored during comparison at level 3. Setting
+ to a later value includes earlier values;
+ e.g. <literal>symbol</literal> also includes
+ <literal>punct</literal> and <literal>space</literal> in the
+ characters to be ignored. Key <literal>ka</literal> must be set to
+ <literal>shifted</literal> and key <literal>ks</literal> must be set
+ to <literal>level3</literal> or lower to take effect.
+ </entry>
+ </row>
+ <row>
+ <entry><literal>co</literal></entry>
+ <entry><literal>emoji</literal>, <literal>phonebk</literal>, <literal>standard</literal>, <replaceable>...</replaceable></entry>
+ <entry><literal>standard</literal></entry>
+ <entry>
+ Collation type. See <xref linkend="icu-external-references"/> for additional options and details.
+ </entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ Defaults may depend on locale. The above table is not meant to be
+ complete. See <xref linkend="icu-external-references"/> for additional
+ options and details.
+ </para>
+ <note>
+ <para>
+ For many collation settings, you must create the collation with
+ <option>DETERMINISTIC</option> set to <literal>false</literal> for the
+ setting to have the desired effect (see <xref
+ linkend="collation-nondeterministic"/>). Additionally, some settings
+ only take effect when the key <literal>ka</literal> is set to
+ <literal>shifted</literal> (see <xref
+ linkend="icu-collation-settings-table"/>).
+ </para>
+ </note>
+ </sect3>
+ <sect3 id="icu-locale-examples">
+ <title>Examples</title>
+ <para>
+ <variablelist>
+ <varlistentry id="collation-managing-create-icu-de-u-co-phonebk-x-icu">
+ <term><literal>CREATE COLLATION "de-u-co-phonebk-x-icu" (provider = icu, locale = 'de-u-co-phonebk');</literal></term>
+ <listitem>
+ <para>German collation with phone book collation type</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="collation-managing-create-icu-und-u-co-emoji-x-icu">
+ <term><literal>CREATE COLLATION "und-u-co-emoji-x-icu" (provider = icu, locale = 'und-u-co-emoji');</literal></term>
+ <listitem>
+ <para>
+ Root collation with Emoji collation type, per Unicode Technical Standard #51
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="collation-managing-create-icu-en-u-kr-grek-latn">
+ <term><literal>CREATE COLLATION latinlast (provider = icu, locale = 'en-u-kr-grek-latn');</literal></term>
+ <listitem>
+ <para>
+ Sort Greek letters before Latin ones. (The default is Latin before Greek.)
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="collation-managing-create-icu-en-u-kf-upper">
+ <term><literal>CREATE COLLATION upperfirst (provider = icu, locale = 'en-u-kf-upper');</literal></term>
+ <listitem>
+ <para>
+ Sort upper-case letters before lower-case letters. (The default is
+ lower-case letters first.)
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="collation-managing-create-icu-en-u-kf-upper-kr-grek-latn">
+ <term><literal>CREATE COLLATION special (provider = icu, locale = 'en-u-kf-upper-kr-grek-latn');</literal></term>
+ <listitem>
+ <para>
+ Combines both of the above options.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ </sect3>
+ <sect3 id="icu-external-references">
+ <title>External References for ICU</title>
+ <para>
+ This section (<xref linkend="icu-custom-collations"/>) is only a brief
+ overview of ICU behavior and language tags. Refer to the following
+ documents for technical details, additional options, and new behavior:
+ </para>
+ <itemizedlist>
+ <listitem>
+ <para>
+ <ulink
+ url="https://www.unicode.org/reports/tr35/tr35-collation.html">Unicode
+ Technical Standard #35</ulink>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <ulink url="https://tools.ietf.org/html/bcp47">BCP 47</ulink>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <ulink url="https://github.com/unicode-org/cldr/blob/master/common/bcp47/collation.xml">CLDR
+ repository</ulink>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <ulink url="https://unicode-org.github.io/icu/userguide/locale/"></ulink>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <ulink url="https://unicode-org.github.io/icu/userguide/collation/api.html"></ulink>
+ </para>
+ </listitem>
+ </itemizedlist>
+ </sect3>
+ </sect2>
</sect1>
<sect1 id="multibyte">
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