Taxonomy Menu: Display Descendants does not work I could not find any good answer to this question online, so I decided to post
  it with the answer I found as it might help some people, I hope so :)


I am using Drupal 7.

In taxonomy menu 1.4 module, if you check option "Display Descendant" , nothing change in your menu.

In taxonomy menu 2.0alpha2 module, if you select the similar option: "Menu path type => Multiple terms" , the items in your menu that have descendants vanish from your menu 

How to get this to work ?
With taxonomy menu 2.0alpha2 if you select multiple you'll see the warning : "Multi-terms path is not available in Drupal by default, which means that you will have to register it using a module like Views for example."

Luckily views provide by default a taxonomy term view to emulate drupal default taxonomy term handling, so you need to activate it. 
But even with this view activated you wont see your menu items, and this is because the path generated by taxonomy menu(ie: taxonomy/term/tid1+tid2 ) is still not handled.

This is because default taxonomy term view handle multiple terms ids argument but does not validate them (WTF !?).

So what you need to do in a nutshell:


  
  In taxonomy menu 2.0alpha2 module, select "Menu path type => Multiple terms"
  Activate taxonomy term view
  In [ Contextual filters =>  Content: Has taxonomy term ID (with depth) => Specify validation criteria => Filter value type ] change to "term IDs separated by , or +"
  


There you go !

ps : I did not try this with taxonomy menu 1.4, anyone ?