str_ucs4_ucs4 Function

   pure function str_ucs4_ucs4(input) result(output)
   !< Convert string of UCS4 kind to UCS4 string, just for convenience in sanitize strings.
   !<
   !<```fortran
   !< use penf
   !< character(len=:, kind=UCS4), allocatable :: string
   !< string = str_ascii(UCS4_'I was UCS4 kind and I am still UCS4')
   !< print "(A)", string
   !<```
   !=> I was UCS4 kind and I am still UCS4 <<<
   character(len=*, kind=UCS4), intent(in)  :: input  !< Input string of UCS4 kind.
   character(len=:, kind=UCS4), allocatable :: output !< Output string of UCS4 kind.

   output = input
   endfunction str_ucs4_ucs4