The Difference Between Hierarchical and Non Hierarchical Taxonomies in WordPress with regards to slugs and public (frontpage) access.
I'm mainly writing this as a reminder for myself but this is how I believe it is organized and I believe it could be helpful if someone ever run into the same issue.
So the main different between hierarchical and non hierarchical taxonomies in WordPress is that hierarchical taxonomies are the typical "category" taxonomy and non hierarchical taxonomy is a "tag" taxonomy.
When you set 'hierarchical' => 'true' or 'false' in the taxonomy settings, you define this behavior which also impacts the access to the taxonomy on the front-end of your WordPress site.
For hierarchical taxonomies, like categories, you may name it like such:
'custom-category'.
Now you can access it example.com/custom-category
And the template for this is archive-custom-category.php in your theme folder.
The template for the single is single-custom-category.php.
Now you could assume, it is the same way for the non hierarchical taxonomy.
Lets say you have a non hierarchical taxonomy called "custom-tag".
But trying to access example.com/custom-tag/ will yield a 404.
Why? Because the taxonomy is non hierarchical and it doesn't have an archive page.
However, you can access example.com/custom-tag/tag-term
which will list all posts associated with the taxonomy that are also "tagged" as "tag-term".
(This is also possible for hierarchical categories: example.com/custom-category/category-term)
Now, you might still want to have a /custom-tag/ "archive", and to achieve this is to create a "page" that you call "custom-tag" with the slug "custom-tag". Leave this blank.
Then create a template in your theme folder with the name: page-custom-tag.php and set the page you created to use this template.
In the template you need to create some code that lists all your posts for the various tags, using the WP_loop and some filtering.
Now you can visit: example.com/custom-tag/ and have it list all your posts assoicated with the custom tag taxonomy.
