code: func AppendNormalizedHeaderKey(dst []byte, key string) []byte {
  	dst = append(dst, key...)
  	normalizeHeaderKey(dst[len(dst)-len(key):], false)
  	return dst
  }
docs: // AppendNormalizedHeaderKey appends normalized header key (name) to dst
  // and returns the resulting dst.
  //
  // Normalized header key starts with uppercase letter. The first letters
  // after dashes are also uppercased. All the other letters are lowercased.
  // Examples:
  //
  //   * coNTENT-TYPe -> Content-Type
  //   * HOST -> Host
  //   * foo-bar-baz -> Foo-Bar-Baz