Hi all!
Regarding this page:
http://www.yiiframework.com/doc-2.0/ext-jui-index.html
Because I don’t have ‘Composer’, I have just added the mentioned line to the composer.json file. But this did not help.
After some tries, I have found the extensions.php file in the /vendor/yiisoft folder. I just extended this file with the yii2-jui folder.
'yiisoft/yii2-jui' =>
array (
'name' => 'yiisoft/yii2-jui',
'version' => '2.0.0.0-beta',
'alias' =>
array (
'@yii/jui' => $vendorDir . '/yiisoft/yii2-jui',
),
),
Then the next problem… The example code mentioned here did not work, because it must be \yii\jui\Accordion in this case:
http://www.yiiframework.com/doc-2.0/yii-jui-accordion.html
And another problem of the manual is that nowhere is mentioned that I first have to get this extension from for example github.com/yiisoft/yii2/tree/master/extensions
After all these steps it worked fine. At least I can see the accordion 
Was the way how I did it totally wrong and therefore the reason, why it did not work easily?
Or was there a big misunderstanding regarding the documentation?
If not, it would be good, if the documentation could be updated accordingly.