The Unicode Case Mapping algorithm defines the process and data to transform text into upper case, lower case or title case.

Since most languages are not bicameral, characters which have no appropriate mapping remain unchanged.

Three case mapping functions are provided as a public API which have their implementations in this module:

• Unicode.String.upcase/2 which will convert text to upper case characters.
• Unicode.String.downcase/2 which will convert text to lower case characters.
• Unicode.String.titlecase/2 which will convert text to title case. Title case means that the first character or each word is set to upper case and all other characters in the word are set to lower case. Unicode.String.split/2 is used to split the string into words before title casing.

Each function operates in a locale-aware manner implementing some basic capabilities:

• Casing rules for the Turkish dotted capital I and dotless small i.
• Casing rules for the retention of dots over i for Lithuanian letters with additional accents.
• Titlecasing of IJ at the start of words in Dutch.
• Removal of accents when upper casing letters in Greek.

There are other casing rules that are not currently implemented such as:

• Titlecasing of second or subsequent letters in words in orthographies that include caseless letters such as apostrophes.
• Uppercasing of U+00DF ß latin small letter sharp s to U+1E9E ẞ latin capital letter sharp s.

Examples

# Basic case transformation
iex> Unicode.String.Case.Mapping.upcase("the quick brown fox")
"THE QUICK BROWN FOX"

# Dotted-I in Turkish and Azeri
iex> Unicode.String.Case.Mapping.upcase("Diyarbakır", :tr)
"DİYARBAKIR"

# Upper case in Greek removes diacritics
iex> Unicode.String.Case.Mapping.upcase("Πατάτα, Αέρας, Μυστήριο", :el)
"ΠΑΤΑΤΑ, ΑΕΡΑΣ, ΜΥΣΤΗΡΙΟ"

# Lower case Greek with a final sigma
iex> Unicode.String.Case.Mapping.downcase("ὈΔΥΣΣΕΎΣ", :el)
"ὀδυσσεύς"

# Title case Dutch with leading dipthong
iex> Unicode.String.Case.Mapping.titlecase("ijsselmeer", :nl)
"IJsselmeer"