code: function findQualifiedChildrenFromList (instances) {
    instances = instances
      .filter(child => !child._isBeingDestroyed)
    return !filter
      ? instances.map(capture)
      : Array.prototype.concat.apply([], instances.map(findQualifiedChildren))
  }
docs: Iterate through an array of instances and flatten it into
  an array of qualified instances. This is a depth-first
  traversal - e.g. if an instance is not matched, we will
  recursively go deeper until a qualified child is found.
  
  @param {Array} instances
  @return {Array}