Modifies the case of an input string to upper- or lowercase or capitalization. The default transformation will be uppercase as in `mb_convert_case` [1].

Possible modes are:

`lower` Transforms the input string to its lowercase representation

`upper` Transforms the input string to its uppercase representation

`capital` Transforms the input string to its first letter upper-cased, i.e. capitalization

`uncapital` Transforms the input string to its first letter lower-cased, i.e. uncapitalization

`capitalWords` Not supported yet: Transforms the input string to each containing word being capitalized

Note that the behavior will be the same as in the appropriate PHP function `mb_convert_case` [1]; especially regarding locale and multibyte behavior.