Detailed answer
Place a nested ul or ol inside the li it describes.
This connects the sublist to its parent item. Source indentation improves readability but cannot create valid structure by itself. Inspect the rendered nesting when a menu or list looks correct visually but behaves unexpectedly in assistive technology.
Example
<ul><li>Forms<ul><li>Labels</li><li>Inputs</li></ul></li><li>Media</li></ul>
Understanding the behavior
A nested list belongs inside the parent li whose content it expands. Placing a second list directly between sibling li elements can produce repaired or misleading structure. Indentation in the source does not establish a parent-child relationship.
Practical implementation notes
Collapse the sub-list conceptually: the parent item should still read sensibly. Use CSS for indentation and markers after the underlying list hierarchy accurately represents the information.
How to check it
Move the sublist inside its owning li and inspect the hierarchy.
Expected result
The subtopics belong to their parent item in the parsed tree.
Watch out: Do not place a sublist directly between sibling list items.
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