This is the most important consideration for selecting a tool to support the project because it gives the project the most flexibility. A built-in support for the method means that the tool has features and functions that are aligned with the SysML-based development method chosen by the project. This can include documentation, context-specific help, templates, wizards, etc. A built-in support for the method can help the project to follow the method more easily and consistently. A mechanism for user-defined extensions to the tool means that the tool allows users to customize or modify the tool according to their needs and preferences. This can include adding new features, changing existing features, creating new views or reports, etc. A mechanism for user-defined extensions to the tool can help the project to tailor the method over the life of the project and adapt to changing requirements or situations. References: https://www.omg.org/ocsmp/ocsmp-adv-exam.htm https://sysml.org/tutorials/sysml-diagram-tutorial/