A PRS must satisfy all stakeholders and be “internally consistent” to be valid.
Requirements must be agreed to by all stakeholders, and must be internally consistent, sufficiently precise, and without error.
In the “real world,” validation generally occurs at an internal level and an external level.
Internal validation: Internal validation is carried out within a company. This usually means the PRS is presented to upper management and validated with respect to corporate strategy, human resources, budgeting, marketing, sales, etc. It is important that all levels of an engineering organization be convinced that a project is well-defined (through a well-written PRS) to ensure there is continued support at all corporate levels for the project.
External validation: External validation is carried out with the client. This usually means the PRS is presented to the customers, clients, regulatory bodies, etc. to ensure that it meets with their approval. In general, any body whose disapproval could adversely affect the design project should be involved at this stage.
Often, some shortcomings in the PRS will be identified in the course of its validation. It is important that any such shortcomings be addressed quickly. To do otherwise endangers the acceptance of the project with many important stakeholders.
There is no real deliverable from this design task. However, whatever PRS is input to the validation process will (hopefully) be “better” as a result. If you've validated your requirements, then no inconsistencies or errors will be found.