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Further clarify documentation for the initcap function

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This is a follow-up for commit c2c2c7e225.  It further clarifies the
following in the initcap function documentation:

 * Document that title case is used for digraphs in specific locales,
 * Reference particular ICU function used,
 * Add note about the purpose of the function.

Discussion: https://postgr.es/m/804cc10ef95d4d3b298e76b181fd9437%40postgrespro.ru
Author: Oleg Tselebrovskiy <o.tselebrovskiy@postgrespro.ru>
Co-authored-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Jeff Davis <pgsql@j-davis.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
This commit is contained in:
Alexander Korotkov
2025-08-26 12:49:44 +03:00
parent f5e0186f86
commit f8ce9ed220
1 changed files with 15 additions and 6 deletions
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21
doc/src/sgml/func/func-string.sgml
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@@ -693,12 +693,21 @@
<returnvalue>text</returnvalue>
</para>
<para>
Converts the first letter of each word to upper case and the
rest to lower case. When using the <literal>libc</literal> locale
provider, words are sequences of alphanumeric characters separated
by non-alphanumeric characters; when using the ICU locale provider,
words are separated according to
<ulink url="https://www.unicode.org/reports/tr29/#Word_Boundaries">Unicode Standard Annex #29</ulink>.
Converts the first letter of each word to upper case (or title case
if the letter is a digraph and locale is <literal>ICU</literal> or
<literal>builtin</literal> <literal>PG_UNICODE_FAST</literal>)
and the rest to lower case. When using the <literal>libc</literal> or
<literal>builtin</literal> locale provider, words are sequences of
alphanumeric characters separated by non-alphanumeric characters;
when using the ICU locale provider, words are separated according to
<ulink url="https://unicode-org.github.io/icu-docs/apidoc/dev/icu4c/ustring_8h.html#a47602e2c2012d77ee91908b9bbfdc063">u_strToTitle ICU function</ulink>.
</para>
<para>
This function is primarily used for convenient
display, and the specific result should not be relied upon because of
the differences between locale providers and between different
ICU versions. If specific word boundary rules are desired,
it is recommended to write a custom function.
</para>
<para>
<literal>initcap('hi THOMAS')</literal>