title: Need clarifications on adding regions dynamically in Marionette
body: <p>I have an application where I need to display metrics.  The application needs to display a separate vertical section for each metric.  When I started this, there were only 5 metrics so I naively created a template with 5 regions, one for each metric I needed to display.   Now, new metrics need to be added and I want to avoid adding "hardcoded" region divs in the template.  I want to refactor this and create the required regions dynamically at startup time based on some configuration data.  </p>
  
  <p>So I have been looking at the latest Marionette release and in question "<a href="https://stackoverflow.com/questions/15690683/dynamically-add-regions-to-marionette-layout">Dynamically add regions to Marionette layout</a>", Derick Bailey mentions that Marionette v1.0 supports dynamic regions in Layouts through addRegion(), as in:</p>
  
  <pre><code>var layout = new MyLayout();
  layout.render()
  layout.addRegion("someRegion", "#some-element");
  layout.someRegion.show(new MyView());
  </code></pre>
  
  <p>I have tried that in my code (using Marionette 1.0.2) and I am not getting it to work.  I don't have a div with id="some-element" in my template and I suspect this could be the reason. I was hoping that Marionette would create that div itself.  </p>
  
  <p>Perhaps my expectation of what dynamically adding a region means is wrong.  So my first question is: when adding regions dynamically to a layout, must the element id passed in the addRegion() function already exist in the layout?</p>
  
  <p>If so, then I am back to the problem of having to "burn" in the template those divs for the regions to attach themselves too.  My follow-up question is then: What is the best way of doing this in a  data-driven fashion?  Is it a matter of writing my own render() function so that the right set of divs get created?  Or perhaps providing my Layout with a model object that will contain data which the template can then iterate through to create the necessary divs?  How do we add regions dynamically to a Layout object if we don't know in advance how many regions we will actually need?</p>