When a plugin is inactive and a site administrator clicks on its deletion link, WordPress checks for the presence of a file called uninstall.php in the plugin directory. If the file exists and the user clicks the OK button to delete, WordPress proceeds with the deletion of all the plugin files and executes the content of the uninstall.php file. This file should contain straight PHP code that deletes all the plugin options and any other content created by the plugin's code. Once executed, the uninstall script will be deleted with the rest of the files.

Looking at the content of the uninstall script, the first few lines of code check for the presence of a constant that WordPress should have set before calling the script. If it is not present, the script will abort immediately for security purposes. This ensures that an external visitor knowing that a certain plugin is installed won't be able to try to delete it. Once the intent has been verified, the rest of the code checks for the existence of the ch2pho_options array that was created in the previous recipe and deletes it. If you created more than one option to store your configuration data, you will need to delete each option with individual calls to the delete_option function.