A segment mark is the specific metacharacter used within D3 items. The segment mark is not actually part of data. Rather, it is used as an item delimiter, and is automatically appended to the end of an item when written to disk.
The segment mark is a reserved character. This means that it cannot be used for any other purpose.
The following table shows the different representations for the segment mark:
| ASCII value | _ |
| Hexadecimal value | ff |
| Decimal value | 255 |