When you create Requirements they are numbered by default with their unique IDs. The default Requirement IDs in modeling tool are hierarchical numbers: 1, 1.1, 1.1.1, etc. As example, see the following figure.
Requirements numbering.
The special validation rules ensures that each of the Requirement ID in your project are unique. For example, it is valuable when working with Teamwork Server or Teamwork Cloud and after commits in the same project appears few Requirements with the same IDs. The validation rules check that and show errors.
If you want a different Requirement numbering than the default, you can customize it manually by using the Element Numbering dialog. However, it is not recommended.
