I realized that the Help Center's search doesn't return results from its "Privileges" section. For example, the list of results from searching "community wiki" doesn't include the "Edit Community Wiki" privilege page.
I'm not sure if this is an oversight or if this is by design. The "Privileges" section does have a non-FAQ structure, so this might or might not explain why it is excluded from the search feature.
I find the "Privileges" pages to be very informational when trying to learn about various site features, such as comments, community wiki, and down-voting. On top of that, the "Privileges" section is a part of the Help Center, so it's counter-intuitive that you can't search that part of the Help Center.