If you think about the classic format for an outline, where Roman Numerals are used for primary divisions, numbers to differentiate sections under primary divisions, lowercase letters to differentiate sub-sections under sections, and lowercase Roman numerals to designate sub-sub-sections, the concept is very much the same. Each of those is a nesting level.
But, as Mr. Turner's reference notes, you can nest things of the same type within each other. You could consider an outline as a sort of list with additional lists nested within it, and the way those lists are differentiated from each other show the nesting level.
Brian - Windows 10 Pro, 64-Bit, Version 20H2, Build 19042
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