code: function prender (vnode, parent, callback) {
    let prev = parent._preactCompatRendered
    if (prev && prev.parentNode !== parent) prev = null
    let out = preactRender(vnode, parent, prev)
    parent._preactCompatRendered = out
    if (typeof callback === 'function') callback()
    return out && out._component
  }
docs: proxy render() since React returns a Component reference.