A skin is a collection of code and resources which can be dropped in to any esoTalk installation to change its appearance. Skins are stored in the addons/skins folder.
Skins are actually just special types of plugins! A skin can technically do everything that a plugin can do, although it is recommended to keep functionality-changing code out of skins. Unlike plugins, only one skin can be activated at a time.
ExampleSkin/ The name of the skin in StudlyCase.
--skin.php The main skin file, where all of the skin's information and logic is located.
--preview.jpg A 250x160 preview which is displayed on the Administration > Appearance page.
Skin details should be added to the ET::$skinInfo array at the top of skin.php. The key must correspond to the name of the skin's folder.
Ideally, you should version-control your skin and create a repository on GitHub. The skin.php file should be at the top-level of the repository; there should be no parent folder.
Skins can be submitted for public listing in the Skins channel on the esoTalk support forum. Read this conversation for skin submission guidelines.