sverify_character_string Function

   elemental function sverify_character_string(s, set, back) result(i)
   !< Return the leftmost (if `back` is either absent or equals false, otherwise the rightmost) character of string that is not
   !< in `set`. If all characters of `string` are found in `set`, the result is zero.
   !<
   !<```fortran
   !< type(string) :: string1
   !< logical      :: test_passed(2)
   !< string1 = 'ell'
   !< test_passed(1) = verify(s='Hello World Hello!', set=string1)==verify(string='Hello World Hello!', set='llo')
   !< test_passed(2) = verify(s='Hello World Hello!', set=string1, back=.true.)==verify(string='Hello World Hello!', set='llo', &
   !<                                                                                   back=.true.)
   !< print '(L1)', all(test_passed)
   !<```
   !=> T <<<
   character(kind=CK, len=*), intent(in)           :: s    !< String.
   type(string),              intent(in)           :: set  !< Searched set.
   logical,                   intent(in), optional :: back !< Start of the last occurrence rather than the first.
   integer                                         :: i    !< Result of the search.

   if (allocated(set%raw)) then
     i = verify(string=s, set=set%raw, back=back)
   else
     i = 0
   endif
   endfunction sverify_character_string