The app/ directory contains all of the theme functionality. Since Sage is a starter theme, it’s okay for you to modify files within app/ to meet the needs of the site you’re building.
The PHP code in Sage is namespaced, so make sure to use namespaced functions and classes.
app/setup.php- Enqueue stylesheets and scripts, register support for theme features with
add_theme_support, register navigation menus and sidebars. See Theme Configuration and Setup.
app/admin.php- Placeholder code for the WordPress theme customizer. You can also use this file for anything related to the WordPress admin.
app/filters.php-
Add WordPress filters in this file. Filters included by default:
body_class— add<body>classesexcerpt_more— add "… Continued" to excerptstemplate_include— enable the theme wrapper- Various filters for the Blade implementation
app/helpers.php-
Helper functions used throughout the theme:
asset_path— used when enqueueing theme assets to provide the correct versioned asset filenamesdisplay_sidebar— used to control displaying the sidebartitle— used to return page titles