ayout file to process

/**
* Function to build layout suggestion
* This function will fetch the .layout file
* and fallback to default page.layout if nothing
* fancy is found
*
* .layout file will follow Drupal per path file
* naming system.
* Example: front page will be page--front.layout
*
* Additional feature outside theme_get_suggestions()
* is per node type layout.
* Example: node type = my_node_type
* then the layout file will be page--node--my-node-type.layout
*
* Processing which layout suggestion to use will
* always follow this rules :
*
* Layout plugin layouts reside in layout plugin directory
* will be always the default page.layout to fallback
*
* Other plugins that have layout file in their plugin
* directory will override Layout Plugin default page.layout
*
* Theme implementing layout must follow this directory
* structure :
* theme_folder/layouts/theme_default - for storing default
* per theme layouts updating theme usually will override
* all layout stored in this folder
*
* theme_folder/layouts/theme_custom - for storing custom
* layout created by user, it is generally a good idea
* to keep files stored in this folder to read only
* so when updating core those files won't got overriden
*
* theme_folder/layouts/theme_dynamic - This will be used
* by other plugins to store their per theme layouts
*
* Layouts file stored in theme_folder/layouts/theme_default
* will overrride the Layout plugins and the other plugin layout
* file
*
* Layout files stored in theme_folder/layouts/theme_custom
* will override the files stored in theme_folder/layouts/theme_default
* and the Layout plugins and the other plugin layout file
*
* Layout files stored in theme_folder/layouts/theme_dynamic
* will override the files stored in theme_folder/layouts/theme_default
* and theme_folder/layouts/theme_custom and also the Layout plugins
* and the other plugin layout file
*
* Layouts stored in variable table will override any layouts stored
* as file if both are in the same suggestion level. File stored layouts
* will prevail against layout stored in variable table, if it has higher
* suggestion level.
*
*/

Taken from the _layout_read_layout_files function who actually reads the .layout files / database.