Existing Post Types:
A "post type" is just a template living intemplates/html/components/forms/.
Every post picks exactly one of them — it's what the Content Template dropdown
selects when you edit a Series.
Create a new Post Type:
Picking an existing type above fills this form in with what that type was made from, so you can change one thing and save it back. Overwrite is ticked for you when you do, since saving it under the same name is the point — change the name and you get a copy instead.<: $forms_dir :>) along with a matching .json sidecar describing
any custom fields, so that the data model knows to keep them when a post is saved.