Add the generic strings to WP_Upgrader::$strings.
Connect to the filesystem.
Download a package.
Unpack a compressed package file.
Install a package.
Run an upgrade/installation.
Toggle maintenance mode for the site.
Get the WP_Theme object for a theme.
Action to perform before installing a theme.
Action to perform following a single theme install.
Action to perform following a single theme update.
Initialize the upgrade strings.
Initialize the installation strings.
Install a theme package.