17 lines
937 B
Text
17 lines
937 B
Text
|
What is Case-Folding?
|
||
|
|
|
||
|
|
In non-Unicode contexts, a common idiom to compare two strings
|
||
|
|
case-insensitively is lc($this) eq lc($that). Before comparing two strings
|
||
|
|
we normalize them to an all-lowercase version. "Hello", "HELLO", and
|
||
|
|
"HeLlO" all have the same lowercase form ("hello"), so it doesn't matter
|
||
|
|
which one we start with; they are all equal to one another after lc.
|
||
|
|
|
||
|
|
In Unicode, things aren't so simple. A Unicode character might have
|
||
|
|
mappings for uppercase, lowercase, and titlecase, and the lowercase mapping
|
||
|
|
of the uppercase mapping of a given character might not be the character
|
||
|
|
that you started with! For example lc(uc("\N{LATIN SMALL LETTER SHARP S"))
|
||
|
|
is "ss", not the eszett we started off with! Case-folding is a part of the
|
||
|
|
Unicode standard that allows any two strings that differ from one another
|
||
|
|
only by case to map to the same "case-folded" form, even when those strings
|
||
|
|
include characters with complex case-mappings.
|