From Joomla! Documentation
< Extension Installer | TriggersRevision as of 21:37, 24 September 2008 by Pasamio
The onBeforeExtensionInstall trigger occurs before the installation of an extension. It has the following parameters:
The method of installation that is occuring, either 'install' or 'discover_install'.
The type of extension that is being installed, for example 'component' or 'plugin'
A copy of the manifest of the extension about to be installed