- Task
- The invoice number contains between 6 and 10 characters and possibly includes an R or a K. In addition, the digits are sometimes separated by a slash: /.
- Solution
- [0-9RK/] {6,10}
- Explanation
-
[0-9RK/]
The invoice number may contain any digit from 0 to 9, the character R and K, as well as a forward slash.