The file structure is incredibly simplistic and easy to understand. Separation of language files are encouraged, especially with the hybrid apps developed today using multiple frameworks and libraries.
Model and controllers are developed in
back >
app
Configurations and routing are in
back >
sys
Database structure for static databases and seeding
back >
db
and Composer / PSR-4 autoload at the project root via
composer.json
Routed views: html/pages
Reused templates: html/templates
Source JS: js · CSS: css · Sass: scss
Build manifest & npm deps: lib/package.json
Built output: public/app.js + app.css
See Packaging.