Control Codes, Private Use, and Combining Marks
| General Category | Stack | Mixed | Memo |
|---|---|---|---|
| Other, Control (Cc) | R | R |  undefined in stacked mode |
| Other, Format (Cf) | R | R | undefined in stacked mode |
| Other, Private Use (Co) | U | U | Bias for East Asian use, since other usage is unknown |
| Other, Surrogate (Cs) | R | R | no need to define? |
| M* | Follows grapheme cluster | ||