Imports for Extensions
Explanation
Installing an extension by importing its XAR file is technically possible but is not the recommended method, because importing an extension's Pages does not bring in the dependencies the extension needs. Use the Extension Manager instead, which resolves them.
Some extensions are nevertheless packaged as XAR files. When importing XWiki Pages, the import process reads the package.xml file contained in the archive. If that file carries an extensionId value, the Importer looks the Extension up in the XWiki Extension Repositories configured in xwiki.properties under the extension.repositories keys.
If the Extension is found in one of those repositories, the Importer registers it as installed on the instance, and it appears in the Extension Manager under "Installed extensions".
FAQ
Why can importing an extension's Pages break the extension?
Because the Pages arrive without the extension's dependencies, and importing them on top of a different version of the same extension can break it through API incompatibilities.
