constructor (owner) {
    super()

    // set when this gets inserted into another virtual element
    this.parent = null
    // set when created by RenderingContext
    this._owner = owner
    // set when ref'd
    this._ref = null
  }
A virtual {@link DOMElement} which is used by the {@link Component} API.

  A VirtualElement is just a description of a DOM structure. It represents a
  virtual DOM mixed with Components. This virtual structure needs to be compiled
  to a {@link Component} to actually create a real DOM element,
  which is done by {@link RenderingEngine}