# `Unicode.String.Case.Folding`
[🔗](https://github.com/elixir-unicode/unicode_string/blob/v2.1.0/lib/unicode/case/folding.ex#L1)

Implements the Unicode Case Folding algorithm.

The intention of case folding is to facilitate
case-insensitive string comparisons. It is not
intended to be a general purpose transformation.

Although case folding does generally use lower
case as its normal form, it is not true for
all scripts and codepoints.  Therefore case
folding should not be used as an alternative
to `String.downcase/1`.

# `fold`

Case fold a string.

Returns a string after applying the Unicode
Case Folding algorithm.

Case folding is intended to suport case
insensitve string comparisons such as that
implemented by `Unicode.String.equals_ignoring_case?/2` which
calls this function on its parameters.

### Arguments

* `string` is any `String.t()`

* `mode or language tag` is either the atoms `:turkic` or `nil`
  or a map that includes the key `:language` with a value that
  is a lowercase atom representing an [ISO 639-1](https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes)
  language code. The [Localize.LanguageTag](https://hexdocs.pm/localize/Localize.LanguageTag.html) which is defined
  as part of [localize](https://hex.pm/packages/localize) is one
  such example. The default is `nil`.

### Returns

  * The case folded string

### Notes

* No normalization is applied to the
  string on either input or output.

* Case folding does not apply any transformation
  to accented characters. `"ü"` will not case fold
  to `"u"` for example.

### Examples

    iex> Unicode.String.Case.Folding.fold("THIS")
    "this"

    iex> Unicode.String.Case.Folding.fold("grüßen")
    "grüssen"

    iex(13)> Unicode.String.Case.Folding.fold("I")
    "i"

    # Turkic languages such as Turkish and Azerbaijani have
    # a dotless lower case "i"
    iex> Unicode.String.Case.Folding.fold("I", :turkic)
    "ı"

    iex> Unicode.String.Case.Folding.fold("I", %{language: :az})
    "ı"

# `fold`

---

*Consult [api-reference.md](api-reference.md) for complete listing*