External Sass tools are NOT used, compilation is done using PHP compiler.
This extension caches compiled CSS code and prevents recompilation if there is no need in it.
A few words about Sass and Compass:
Sass is an extension of CSS that adds power and elegance to the basic language. It allows you to use variables, nested rules, mixins, inline imports, and more, all with a fully CSS-compatible syntax. Sass helps keep large stylesheets well-organized, and get small stylesheets up and running quickly.
Compass is an open-source CSS authoring framework which uses the Sass stylesheet language to make writing stylesheets powerful and easy.
Allow to register and publish compiled CSS files inside specific published directory to allow using of relative references in CSS for images, fonts and other published files
Add compilerOutputFormatting component option, allow to switch between simple, nested and compressed (Pavel Volyntsev)
Change default value of the writableDirectoryPermissions component option from 0644 to 0777. It should prevent permission errors on some Linux servers
Fix CAssetManager::publish() call - pass $hashByName value used in Yii::app()->sass->publish() and Yii::app()->sass->register() methods
Remove deprecated PHPUnit "strict" setting
Do not use unstable (dev-master) version of scssphp compiler anymore when Composer is used to install yii-sass extension
Make installation via Composer easier - "minimum-stability" setting is not needed anymore
Add "writableFilePermissions" option (defaults to 0666), fix file permissions issues with certain umask settings in OS by calling chmod for created/updated files, always call chmod for writable directories
Add “defaultHashByName” setting which allows to set a default “$hashByName” value for all plugin’s methods