The types of section a page can hold (SectionType): every sections/{name}.schema.json that has its sections/{name}.phtml, in the folders of Pages::$templates. A folder listed first wins: an application replaces a type of mmo.editor's own by writing one of the same name in its folder.
class MMO\editor\cms\SectionTypes
Namespace
MMO\editor\cms
$types = new SectionTypes(['{root}/templates', __DIR__ . '/../../templates']);
$types->get('hero')?->getDefaults();
the files of $folder whose name ends with $suffix, sorted: scandir() and not glob(), which finds nothing in a phar -- a release runs its application's section types from one
the css of the sections: every folder's sections/sections.css then its types' own (sections/{name}.css), mmo.editor's folder first and the application's after it, so that an application restyles the sections without writing them again
these types, and $type -- which replaces one of the same name -- with $styles after the others': what the section-type editor previews before it is saved