Making a requirement a subrequirement of another requirement (SysML)
You can set up subrequirements on a Requirement Diagram through Requirement Containment Links.
To make a requirement a subrequirement of another requirement on a requirement diagram:
1. Add the two Requirements to the Requirement Diagram.
2. On the diagram's tab, click the 
Contained Requirement Link button.
Contained Requirement Link button.3. Click the parent Requirement, and then click the subrequirement.
To make a requirement a subrequirement of another requirement through a Modeler pane:
Drag the Requirement you want to be the subrequirement to the Requirement you want to be the parent.