title: PlantUML: overlapping activations (multiple threads)
body: <p>I am trying to show overlapping activations in my sequence diagram (I am using PlantUML) but they are showing as nested activations:</p>
  
  <p>For example:</p>
  
  <pre><code>@startuml
  participant T1
  participant T2
  participant Main
  
  T1 -&gt; Main ++ #red: start
  T2 -&gt; Main ++ #yellow: start
  
  Main --&gt; T1 -- #red : done
  Main --&gt; T2 -- #yellow : done
  
  @enduml
  </code></pre>
  
  <p>This will show nested red/yellow activations while I was expecting red to finish before yellow.</p>
  
  <p>Is this supported? Am I doing something wrong?</p>
  
  <p>Thanks!</p>