Extensions
Extension Manager support various types of extensions.
Generic
Those are the various states each type of extension can have inside XWiki.
Core: readonly extension loaded by the application server (generlaly coming from the XWiki WAR or provided by the application server itself)
Local: all extensions that were downloaded at some point and kept in a special local folder of extenions
Installed: local extensions which are actually installed and usable in the XWiki instance
Typed
Those are typed extensions for which a special handler and related tools are provided to deal with the differences (how to actually install it, etc.).
JAR: extensions associated with a Java JAR file
XAR: XWiki packages containing wiki pages
WebJar: Java JAR files but containing web resources (JS/CSS/Less)
empty: extensions without any associated file
