How does Luma theme home page work?

Question

I understand that the home page content is defined in block home-page-block, and I can edit that and see changes appear in the browser.

However, what I don't understand is:

1. What bit of theme/template/code invokes home-page-block in the first place. (I am searching everything I can think of, and nothing...)

2. The relationship, if any, to Content > Pages > Home Page, which is blank. And furthermore, I can edit Home Page, it does not show up as the home page, but does show up at [mysite.com]/home/.

What am I missing?

Edit: Partial understanding

Based on reading docs and source code, the diagram shows some of the contributors to the construction of the Luma home page.

Among mysteries solved:

• in the Content > Widget configuration page, the list of pages offered as targets comes from Magento consolidating all the page_types.xml files from all modules.

• On that same admin page, the list of target Containers appears to come from module-theme/view/frontend/layout/default.xml. (Not sure if it changes when different target page is selected.)

Nagging Questions

How are some of the things in the above diagram specified, based on the requested route '/'?

A. Routing: '/' Route matching patterns are normally specified in routes.xml files for each module. But where is the routes.xml for '/'? And how does module-cms get invoked (whose page_types.xml shows it handles "CMS Home Page"/cms_index_index). How does routing result in a requested page type of cms_index_index?

B1. The seemingly corresponding layout, /vendor/magento/module-cms/view/frontend/layout/cms_index_index.xml shows an empty body. How does that relate?

B2. Instead, the delivered page appears to have the structure of /vendor/magento/module-theme/view/frontend/layout/default.xml. (Deduced from it being the only file with a container called "Main Content Area", as targeted by Widget "Home Page") What precipitates invocation of default.xml?

C. Why is the Luma home page implemented with a Widget and a Block and not simply a Page?

Edit 2

I pursued part of this question here: How does home page routing work?

Answer 1

Pretty straight relation which invokes home-page-block, is Widgets.

1. Content -> Widgets -> Now click on Home Page widget. Storefront Properties -> Layout Updates -> specific page Widget Options -> Block > Home Page Block.

2. You can set/change CMS page by Stores-> Configuration-> General-> Web-> Default Pages-> CMS Home Page You can select the page by title.

   By default the page is Home Page

3. Module-Widget Module is responsible for all the code, a lot more questions can be covered if you observe the below file.

   Magento root/vendor/magento/module-widget/view/adminhtml/templates/instance/edit/layout.phtml

Where does it get its list of Pages ?

As on the above if you go to line 136

   $block->getLayoutsChooser();

  /vendor/magento/module-widget/Block/Adminhtml/Widget/Instance/Edit/Tab/Main/Layout.php

File contains

    public function getLayoutsChooser()
    {
        $chooserBlock = $this->getLayout()->createBlock(
            'Magento\Widget\Block\Adminhtml\Widget\Instance\Edit\Chooser\Layout'
 // Setting other variables
        )
   }

/vendor/magento/module-widget/Block/Adminhtml/Widget/Instance/Edit/Chooser/Layout.php

The below function will return the pages.

protected function _beforeToHtml()
{
    if (!$this->getOptions()) {
        $this->addOption('', __('-- Please Select --'));
        $pageTypes = $this->_config->getPageTypes();
        $this->_addPageTypeOptions($pageTypes);
    }
    return parent::_beforeToHtml();
}

Where the container can be rendered ?

in the layout.phtml $block->getDisplayOnContainers(); is responsible for getting all containers.

What is the container means ?

Containers are type of blocks for structured design which follows design fallback. Quick working example for create container.

which says "CMS Static Block Default Template". What's its role ?

Means it will follow static block default design

<input type="hidden" value="widget/static_block/default.phtml" name="widget_instance[0][pages][template]" disabled="disabled">

/vendor/magento/module-widget/view/frontend/layout/default.xml