code: function (embedder, frameName, guest, options) {
    // When |embedder| is destroyed we should also destroy attached guest, and if
    // guest is closed by user then we should prevent |embedder| from double
    // closing guest.
    const guestId = guest.webContents.id
    const closedByEmbedder = function () {
      guest.removeListener('closed', closedByUser)
      guest.destroy()
    }
    const closedByUser = function () {
      embedder._sendInternal('ELECTRON_GUEST_WINDOW_MANAGER_WINDOW_CLOSED_' + guestId)
      embedder.removeListener('current-render-view-deleted', closedByEmbedder)
    }
    embedder.once('current-render-view-deleted', closedByEmbedder)
    guest.once('closed', closedByUser)
    if (frameName) {
      frameToGuest.set(frameName, guest)
      guest.frameName = frameName
      guest.once('closed', function () {
        frameToGuest.delete(frameName)
      })
    }
    return guestId
  }
docs: Setup a new guest with |embedder|