Which of the following statements is true?

The statement that SAIL was designed to enhance user interface creation is accurate and highlights the primary purpose of the SAIL (Self-Assembling Interface Layer) framework within Appian. SAIL provides a robust set of components and features that allow developers to create dynamic, responsive, and user-friendly interfaces for applications. It facilitates a more streamlined approach to UI design by enabling the reuse of components, ensuring consistency across interfaces, and allowing for a responsive design that adapts to different screen sizes and devices.

In contrast, the other options present misunderstandings of Appian's functionalities. For instance, not all functions in Appian can work without parameters; many require specific inputs to execute properly. While syntax errors can be problematic, adding comments does not resolve them; instead, comments serve to explain code or clarify logic without affecting execution. Finally, literal values can indeed be used in expression rules, allowing for direct input of values into computations or conditions.

Therefore, the focus of SAIL on enhancing user interface creation directly captures an essential element of its design philosophy and practical application within the Appian environment.