code: function createScope(env, parentScope) {
      if (parentScope) {
        return env.hooks.createChildScope(parentScope);
      } else {
        return env.hooks.createFreshScope();
      }
    }
docs: Host Hook: createScope
  
  @param {Scope?} parentScope
  @return Scope
  
  Corresponds to entering a new HTMLBars block.
  
  This hook is invoked when a block is entered with
  a new `self` or additional local variables.
  
  When invoked for a top-level template, the
  `parentScope` is `null`, and this hook should return
  a fresh Scope.
  
  When invoked for a child template, the `parentScope`
  is the scope for the parent environment.
  
  Note that the `Scope` is an opaque value that is
  passed to other host hooks. For example, the `get`
  hook uses the scope to retrieve a value for a given
  scope and variable name.