What is the correct semantic in this case:

  <service name="JVM Definition"
           singleton="true"
           createDeletePolicy="both">

I would like to be able to have exactly 1 child resource of that type below a given parent.

In the plugin code, I can of course prevent the creation of a 2nd child by 
looking at the list of existing children.

It would be good though, if that logic could also run in the server/UI so that
the Create Child->JVM Definition would be greyed out if one child is already there.

Also it looks like the "singleton" flag just tells the UI to not put the resource in a folder when there
are more than one, but directly below the parent 


In the screen shot, both 'bla' and 'default' are such singleton JVM Definitions

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