Final answer:
The quality attribute described by limiting function call nesting to two levels is readability and maintainability, which ensures better code quality in software development.
Step-by-step explanation:
The statement "Function calls shall not be nested more than two levels deep" describes the quality attribute of readability and maintainability in software development. This guideline helps to prevent overly complex code, which can be difficult to understand and maintain. When a function call is nested inside another function call, and this pattern continues beyond two levels, the code can become confusing and error-prone. Adhering to this rule makes it easier for developers to read and understand the code, which in turn facilitates debugging and future modifications. It is a common practice in software engineering to maintain such standards to ensure code quality.