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-== Case Mapping
-
-Some string-oriented methods use case mapping.
-
-In String:
-
-- String#capitalize
-- String#capitalize!
-- String#casecmp
-- String#casecmp?
-- String#downcase
-- String#downcase!
-- String#swapcase
-- String#swapcase!
-- String#upcase
-- String#upcase!
-
-In Symbol:
-
-- Symbol#capitalize
-- Symbol#casecmp
-- Symbol#casecmp?
-- Symbol#downcase
-- Symbol#swapcase
-- Symbol#upcase
-
-=== Default Case Mapping
-
-By default, all of these methods use full Unicode case mapping,
-which is suitable for most languages.
-See {Unicode Latin Case Chart}[https://www.unicode.org/charts/case].
-
-Non-ASCII case mapping and folding are supported for UTF-8,
-UTF-16BE/LE, UTF-32BE/LE, and ISO-8859-1~16 Strings/Symbols.
-
-Context-dependent case mapping as described in
-{Table 3-17 of the Unicode standard}[https://www.unicode.org/versions/Unicode13.0.0/ch03.pdf]
-is currently not supported.
-
-In most cases, case conversions of a string have the same number of characters.
-There are exceptions (see also +:fold+ below):
-
-  s = "\u00DF" # => "ß"
-  s.upcase     # => "SS"
-  s = "\u0149" # => "ŉ"
-  s.upcase     # => "ʼN"
-
-Case mapping may also depend on locale (see also +:turkic+ below):
-
-  s = "\u0049"        # => "I"
-  s.downcase          # => "i" # Dot above.
-  s.downcase(:turkic) # => "ı" # No dot above.
-
-Case changes may not be reversible:
-
-  s = 'Hello World!' # => "Hello World!"
-  s.downcase         # => "hello world!"
-  s.downcase.upcase  # => "HELLO WORLD!" # Different from original s.
-
-Case changing methods may not maintain Unicode normalization.
-See String#unicode_normalize).
-
-=== Options for Case Mapping
-
-Except for +casecmp+ and +casecmp?+,
-each of the case-mapping methods listed above
-accepts optional arguments, <tt>*options</tt>.
-
-The arguments may be:
-
-- +:ascii+ only.
-- +:fold+ only.
-- +:turkic+ or +:lithuanian+ or both.
-
-The options:
-
-- +:ascii+:
-  ASCII-only mapping:
-  uppercase letters ('A'..'Z') are mapped to lowercase letters ('a'..'z);
-  other characters are not changed
-
-    s = "Foo \u00D8 \u00F8 Bar" # => "Foo Ø ø Bar"
-    s.upcase                    # => "FOO Ø Ø BAR"
-    s.downcase                  # => "foo ø ø bar"
-    s.upcase(:ascii)            # => "FOO Ø ø BAR"
-    s.downcase(:ascii)          # => "foo Ø ø bar"
-
-- +:turkic+:
-  Full Unicode case mapping, adapted for the Turkic languages
-  that distinguish dotted and dotless I, for example Turkish and Azeri.
-
-    s = 'Türkiye'       # => "Türkiye"
-    s.upcase            # => "TÜRKIYE"
-    s.upcase(:turkic)   # => "TÜRKİYE" # Dot above.
-
-    s = 'TÜRKIYE'       # => "TÜRKIYE"
-    s.downcase          # => "türkiye"
-    s.downcase(:turkic) # => "türkıye" # No dot above.
-
-- +:lithuanian+:
-  Not yet implemented.
-
-- +:fold+ (available only for String#downcase, String#downcase!,
-  and Symbol#downcase):
-  Unicode case folding,
-  which is more far-reaching than Unicode case mapping.
-
-    s = "\u00DF"      # => "ß"
-    s.downcase        # => "ß"
-    s.downcase(:fold) # => "ss"
-    s.upcase          # => "SS"
-
-    s = "\uFB04"      # => "ﬄ"
-    s.downcase        # => "ﬄ"
-    s.upcase          # => "FFL"
-    s.downcase(:fold) # => "ffl"