public static Version getPriorToServerVersion( Path pluginDir )
    {
        final String value = getElementValue( pluginDir, "/plugin/priorToServerVersion" );
        if ( value == null || value.trim().isEmpty() )
        {
            return null;
        }

        return new Version( value );
    }
Returns the server version up, but not including, in which this plugin can run within. The value is retrieved from
the plugin.xml file of the plugin. If the value could not be found, {@code null} will be returned.

@param pluginDir the path of the plugin directory.
@return the plugin's maximum server version (possibly null).
xmppserver/src/main/java/org/jivesoftware/openfire/container/PluginMetadataHelper.java