The LowerCase(s) calling sequence changes each alphabetic character in the string s to lowercase and returns the result in a new string. The string s remains unchanged.

The UpperCase(s) calling sequence changes each alphabetic character in the string s to uppercase and returns the result in a new string. The string s remains unchanged.

The OtherCase(s) calling sequence changes each alphabetic character in the string s to the opposite case and returns the result in a new string. The string s remains unchanged.

See StringTools[IsLower] and StringTools[IsUpper] for definitions of lower and uppercase characters.

These commands all accept an optional, second argument rng, a range that specifies a substring of the input s to be affected by the operation. Only characters within the given range are changed.

All of the StringTools package commands treat strings as (null-terminated) sequences of $8$-bit (ASCII) characters.  Thus, there is no support for multibyte character encodings, such as unicode encodings.

$\mathrm{with}\left(\mathrm{StringTools}\right)\:$

$\mathrm{LowerCase}\left(''''\right)$

$\mathrm{LowerCase}\left(''ABC''\right)$

$''abc''$

$\mathrm{LowerCase}\left(''ABC;!def''\right)$

$''abc;!def''$

$\mathrm{LowerCase}\left(''Impedance\; of\; Free\; Space''\right)$

$''impedance\; of\; free\; space''$

$\mathrm{LowerCase}\left(''ABCDEFGHIJ''\,3..8\right)$

$''ABcdefghIJ''$

$\mathrm{UpperCase}\left(''''\right)$

$\mathrm{UpperCase}\left(''abc''\right)$

$''ABC''$

$\mathrm{UpperCase}\left(''abc;!DEF''\right)$

$''ABC;!DEF''$

$\mathrm{UpperCase}\left(''Totally\; Random''\right)$

$''TOTALLY\; RANDOM''$

$\mathrm{UpperCase}\left(''abcdefghij''\,3..-2\right)$

$''abCDEFGHIJ''$

$\mathrm{OtherCase}\left(''''\right)$

$\mathrm{OtherCase}\left(''abc''\right)$

$''ABC''$

$\mathrm{OtherCase}\left(''DEF''\right)$

$''def''$

$\mathrm{OtherCase}\left(''abc;DEF''\right)$

$''ABC;def''$

$\mathrm{OtherCase}\left(''The\; Higher,\; The\; Fewer!''\right)$

$''tHE\; hIGHER,\; tHE\; fEWER!''$

$s≔\mathrm{LowerCase}\left(''abcDEF''\right)$

$s≔''abcdef''$

$\mathrm{UpperCase}\left(s\right)$

$''ABCDEF''$

$\mathrm{LowerCase}\left(\mathrm{UpperCase}\left(\mathrm{LowerCase}\left(''abcDEF''\right)\right)\right)$

$''abcdef''$

$\mathrm{OtherCase}\left(\mathrm{OtherCase}\left(''abcDEF''\right)\right)$

$''abcDEF''$