(CharacterLength=
  length c
.     0:?length
    & @( !arg
       :   ?
           ( %?c
           & utf$!c:?k
           & 1+!length:?length
           & ~
           )
           ?
       )
  | !length
);

out$CharacterLength$𝔘𝔫𝔦𝔠𝔬𝔡𝔢