What does a requirements specification include?

A requirements specification is a comprehensive document that outlines the necessary criteria for a system, including both functional and non-functional requirements. It typically details how the system will interact with users and other systems, ensuring clarity in understanding the project's needs and expectations. This includes defining what the system is required to do (functional requirements) as well as how the system should perform under certain conditions (non-functional requirements), such as performance, security, and usability.

The inclusion of a description of system interactions is critical because it helps developers and stakeholders visualize how different components within the system will communicate and operate together. Non-functional requirements complement functional requirements by addressing aspects that affect user experience and system efficiency, which are just as essential for a complete understanding of the project's goals.

In contrast, providing only functional requirements, as suggested by one of the other options, would lack the necessary context for assessing the system's performance and user interactions. Additionally, a detailed code implementation plan does not belong in a requirements specification, as it focuses on how to build the system rather than what needs to be built. Lastly, while hardware and software specifications can be part of the overall project documentation, they do not encompass the full scope of requirements as outlined in the correct choice.