ICU normalization token filter

Normalizes characters as explained here. It registers itself as the icu_normalizer token filter, which is available to all indices without any further configuration. The type of normalization can be specified with the name parameter, which accepts nfc, nfkc, and nfkc_cf (default).

Which letters are normalized can be controlled by specifying the unicode_set_filter parameter, which accepts a UnicodeSet.

You should probably prefer the Normalization character filter.

Here are two examples, the default usage and a customised token filter:

PUT icu_sample
{
  "settings": {
    "index": {
      "analysis": {
        "analyzer": {
          "nfkc_cf_normalized": { 
            "tokenizer": "icu_tokenizer",
            "filter": [
              "icu_normalizer"
            ]
          },
          "nfc_normalized": { 
            "tokenizer": "icu_tokenizer",
            "filter": [
              "nfc_normalizer"
            ]
          }
        },
        "filter": {
          "nfc_normalizer": {
            "type": "icu_normalizer",
            "name": "nfc"
          }
        }
      }
    }
  }
}

	Uses the default `nfkc_cf` normalization.
	Uses the customized `nfc_normalizer` token filter, which is set to use `nfc` normalization.

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