>>717
(info "(elisp)Regexp Backslash")
| `\cC'
| matches any character whose category is C. Here C is a character
| that represents a category: thus, `c' for Chinese characters or
| `g' for Greek characters in the standard category table.

というのがあるんだけど、C の説明が無いね。
\cj だった気がするけど、不具合があるかもしれん。

ASCII 以外だと、↓これはいかが？
(info "(elisp)Char Classes")
| `[:multibyte:]'
| This matches any multibyte character (*note Text
| Representations::).