layout_list_page in core/modules/layout/layout.admin.inc

Output a list of layouts that are managed.

layout_page_menu_item in core/modules/layout/layout.module

Create a menu item for Layout-provided pages.

layout_provides_path in core/modules/layout/layout.module

Check if a path is provided by Layout module, as in a custom layout path.

layout_removal_removes_page in core/modules/layout/layout.admin.inc

Determines whether the deletion or disabling of this layout would remove the page at its path or additional paths.

layout_route_handler in core/modules/layout/layout.module

Route handler callback; Execute the current route item or wrap in a layout.

system_block_view in core/modules/system/system.module

Implements hook_block_view().