[[character-folding]] === Unicode Character Folding In the same way as the `lowercase` token filter is a good starting point for many languages((("Unicode", "character folding")))((("tokens", "normalizing", "Unicode character folding"))) but falls short when exposed to the entire tower of Babel, so the <<asciifolding-token-filter,`asciifolding` token filter>> requires a more effective Unicode _character-folding_ counterpart((("character folding"))) for dealing with the many languages of the world.((("asciifolding token filter"))) The `icu_folding` token filter (provided by the <<icu-plugin,`icu` plug-in>>) does the same job as the `asciifolding` filter, ((("icu_folding token filter")))but extends the transformation to scripts that are not ASCII-based, such as Greek, Hebrew, Han, conversion of numbers in other scripts into their Latin equivalents, plus various other numeric, symbolic, and punctuation transformations. The `icu_folding` token filter applies Unicode normalization and case folding from `nfkc_cf` automatically,((("nfkc_cf normalization form"))) so the `icu_normalizer` is not required: [source,js] -------------------------------------------------- PUT /my_index { "settings": { "analysis": { "analyzer": { "my_folder": { "tokenizer": "icu_tokenizer", "filter": [ "icu_folding" ] } } } } } GET /my_index/_analyze?analyzer=my_folder ١٢٣٤٥ <1> -------------------------------------------------- <1> The Arabic numerals `١٢٣٤٥` are folded to their Latin equivalent: `12345`. If there are particular characters that you would like to protect from folding, you can use a http://icu-project.org/apiref/icu4j/com/ibm/icu/text/UnicodeSet.html[_UnicodeSet_] (much like a character class in regular expressions) to specify which Unicode characters may be folded. For instance, to exclude the Swedish letters `å`, `ä`, `ö`, ++Å++, `Ä`, and `Ö` from folding, you would specify a character class representing all Unicode characters, except for those letters: `[^åäöÅÄÖ]` (`^` means _everything except_).((("swedish_folding filter")))((("swedish analyzer"))) [source,js] -------------------------------------------------- PUT /my_index { "settings": { "analysis": { "filter": { "swedish_folding": { <1> "type": "icu_folding", "unicodeSetFilter": "[^åäöÅÄÖ]" } }, "analyzer": { "swedish_analyzer": { <2> "tokenizer": "icu_tokenizer", "filter": [ "swedish_folding", "lowercase" ] } } } } } -------------------------------------------------- <1> The `swedish_folding` token filter customizes the `icu_folding` token filter to exclude Swedish letters, both uppercase and lowercase. <2> The `swedish` analyzer first tokenizes words, then folds each token by using the `swedish_folding` filter, and then lowercases each token in case it includes some of the uppercase excluded letters: ++Å++, `Ä`, or `Ö`.