code: func (p Pages) ByWeight() Pages {
  	const key = "pageSort.ByWeight"
  	pages, _ := spc.get(key, pageBy(DefaultPageSort).Sort, p)
  	return pages
  }
docs: // ByWeight sorts the Pages by weight and returns a copy.
  //
  // Adjacent invocations on the same receiver will return a cached result.
  //
  // This may safely be executed  in parallel.