What does the aria-level property define?

The aria-level property defines the hierarchical level of an element within a document structure, particularly in contexts where elements are organized in a tree format, such as headings or lists. It indicates the nesting level of the element relative to its parent elements. For example, in an outline of a document, a top-level heading would have an aria-level of 1, while a subheading under it would have an aria-level of 2. This relationship helps assistive technologies, such as screen readers, to communicate the organization and context of content effectively to users with disabilities, enabling them to navigate complex documents more efficiently.

Other options do not correctly describe the function of aria-level. It does not relate to text complexity, style elements, or the overall readability of content, which are different aspects of document accessibility and design.