Which of the following is not an IREB validation quality criteria for specification content?

Understandability is not an IREB validation quality criteria for specification content. The IREB framework focuses on several key validation criteria to ensure that requirements specifications are effective and useful.

Verifiability ensures that each requirement can be tested or measured against real-world scenarios, meaning that it can be proven true or false. Necessity pertains to whether each requirement is essential for the project goals, preventing unnecessary features that don't contribute to value. Completeness of the document evaluates whether all necessary requirements are included, ensuring no critical aspects are missing.

While understandability is important for effective communication of the requirements, it is not classified as a validation criterion within the IREB framework. This distinction is significant, as the IREB focuses on the objective and measurable aspects of requirements validation rather than the subjective nature of how easily those requirements can be comprehended.