关于format函数的一个奇怪问题

Emacs-general
16 
(length (format "%3s" "'")) ;; => 3
(length (format "%3s" "~")) ;; => 3
(length (format "%3s" "@")) ;; => 3
(length (format "%3s" "ቷ")) ;; => 3
(length (format "%3s" "步")) ;; => 2
(length (format "%3s" "〈")) ;; => 2
(length (format "%3s" "💏")) ;; => 2
(length (format "%3s" "ㅿ")) ;; => 2
(length (format "%3s" "͈")) ;; => 4
(length (format "%3s" "𞥆")) ;; => 4
(length (format "%3s" "​")) ;; => 4 ;; ZERO WIDTH SPACE

估计是按 unicode 的显示宽度来的