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.
Upgrade a theme.
Turn on maintenance mode before attempting to upgrade the current theme.
Turn off maintenance mode after upgrading the current theme.
Delete the old theme during an upgrade.
Action to perform before installing a theme.
Action to perform following a single theme install.