code: func (ps pageStatePages) findPagePos(page *pageState) int {
  	for i, x := range ps {
  		if x.File().Filename() == page.File().Filename() {
  			return i
  		}
  	}
  	return -1
  }
docs: // findPagePos Given a page, it will find the position in Pages
  // will return -1 if not found