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Fix documentation of regular expression character-entry escapes.

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The docs claimed that \uhhhh would be interpreted as a Unicode value
regardless of the database encoding, but it's never been implemented
that way: \uhhhh and \xhhhh actually mean exactly the same thing, namely
the character that pg_mb2wchar translates to 0xhhhh.  Moreover we were
falsely dismissive of the usefulness of Unicode code points above FFFF.
Fix that.

It's been like this for ages, so back-patch to all supported branches.
This commit is contained in:
Tom Lane 2015-09-16 14:50:12 -04:00
parent 698c7a3bc0
commit f7eeb324e7
1 changed files with 17 additions and 4 deletions
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21
doc/src/sgml/func.sgml
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@ -4148,7 +4148,7 @@ SELECT foo FROM regexp_split_to_table('the quick brown fox', E'\\s*') AS foo;
<entry> <literal>\e</> </entry>
<entry> the character whose collating-sequence name
is <literal>ESC</>,
or failing that, the character with octal value 033 </entry>
or failing that, the character with octal value <literal>033</> </entry>
</row>
<row>
@ -4174,15 +4174,17 @@ SELECT foo FROM regexp_split_to_table('the quick brown fox', E'\\s*') AS foo;
<row>
<entry> <literal>\u</><replaceable>wxyz</> </entry>
<entry> (where <replaceable>wxyz</> is exactly four hexadecimal digits)
the UTF16 (Unicode, 16-bit) character <literal>U+</><replaceable>wxyz</>
in the local byte ordering </entry>
the character whose hexadecimal value is
<literal>0x</><replaceable>wxyz</>
</entry>
</row>
<row>
<entry> <literal>\U</><replaceable>stuvwxyz</> </entry>
<entry> (where <replaceable>stuvwxyz</> is exactly eight hexadecimal
digits)
reserved for a hypothetical Unicode extension to 32 bits
the character whose hexadecimal value is
<literal>0x</><replaceable>stuvwxyz</>
</entry>
</row>
@ -4231,6 +4233,17 @@ SELECT foo FROM regexp_split_to_table('the quick brown fox', E'\\s*') AS foo;
Octal digits are <literal>0</>-<literal>7</>.
</para>
<para>
Numeric character-entry escapes specifying values outside the ASCII range
(0-127) have meanings dependent on the database encoding. When the
encoding is UTF-8, escape values are equivalent to Unicode code points,
for example <literal>\u1234</> means the character <literal>U+1234</>.
For other multibyte encodings, character-entry escapes usually just
specify the concatenation of the byte values for the character. If the
escape value does not correspond to any legal character in the database
encoding, no error will be raised, but it will never match any data.
</para>
<para>
The character-entry escapes are always taken as ordinary characters.
For example, <literal>\135</> is <literal>]</> in ASCII, but