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Caseless Matching (Unicode)
Last updated at 1:26 pm UTC on 10 December 2015
From The Unicode Standard

Caseless matching is implemented using case folding,
which is the process of mapping characters of different case to a
single form, so that case differences in strings are erased.

Case folding allows for fast caseless matches in lookups because only binary comparison is required. It is more than just conversion to

For example, it correctly handles cases such as the Greek sigma, so that “xy{|” and “butu” will match.
Normally, the original source string is not replaced by the folded string because that substitution may erase important information. For example, the name “Marco di Silva” would be folded to “marco di silva,” losing the information regarding which letters are capitalized. Typically, the original string is stored along with a case-folded version for fast

file in the Unicode Character Database is used to perform locale-independent case folding.