Should a custom filter page be index.md or _index.md?

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1

With the following content structure, what is the correct index file name to use for the folders non-fiction and fiction, a leaf bundle with index.md or a page bundle with _index.md?

content
   |-- books
        |-- non-fiction
              |-- index.md or _index.md?
        |-- fiction
              |-- index.md or _index.md?
        |-- _index.md
        |-- book1.md
        |-- book2.md

I use a custom template, books/filter.html for non-fiction and fiction to show the list books that are fiction and non-fiction. Basically, a custom variation instead of using taxonomies.

As these pages show a list of items, should I be using _index.md? No other resources except the index file name will be in each folder.

Or would it be more correct to change the structure and do the following:

content
   |-- books
        |-- non-fiction.md
        |-- fiction.md
        |-- _index.md
        |-- book1.md
        |-- book2.md
2

Depends on how to want to categorize things. Personally I’d either

(1) make a section for each type (fiction, non-fiction, etc) and file book pages accordingly
or
(2) place all book pages under books and tag each page in front matter with genre

3

Thanks.

Option 1 isn’t possible. With option 2, the problem would be that I won’t have control over genre metadata, title and metadescription tags, without writing if else statements. That’s why I’m looking into the above structure of using either index.md or _index.md.