Extension Installer/File Formats
From Joomla! Documentation
Installer File Formats
Joomla! 1.5 Notes
Joomla! 1.5 changes the 'root' tag used for installation packages. In Joomla! 1.0 and earlier, the root tag used was 'mosinstall', Joomla! 1.5 changes this to 'install'. Joomla! 1.5 introduced the concept of site and administrator languages enabling Joomla! to be fully translated and this was reflected in the language installer. Joomla! 1.5 also renamed 'mambots' to 'plugins', which has again been reflected in the installer file formats. Mambots and plugins should be interchangeable however the usage of 'mambot' as an install type has been deprecated and is not valid in the Joomla! 1.6 release.
Joomla! 1.6 Notes
The usage of "install" as the root tag has been deprecated in favour of "extension". This has been done to avoid conflicts with of tags in some formats as well as to better reflect the nature of the file format.
Joomla! 1.6 features a new trigger system for all extensions similar to the "installfile"/"uninstallfile" feature that components have in 1.0/1.5 releases. Triggers available include preflight, installer, update, discover, postflight, uninstall. All triggers are supplied with a reference to the installer instance and the 'preflight' and 'postflight' triggers also have a parameter specifying the trigger they surround (e.g. 'install').
Joomla! 1.6 Notes
Joomla! 1.6 deprecates the usage of "installfile" and "uninstallfile" tags in favour of the new "scriptfile" tag. Additional to this the "com_install" and "com_uninstall" methods are deprecated in favour of a installation class (e.g. ExtensionNameManifest).
Languages are available to be installed in either the site, the administrator or both. This is controlled through the use of a 'client' tag which specifies the target application. The virtual client 'both' was added in Joomla! 1.5.4 to allow one language package to install language files in both the 'site' and 'administrator'.