19   constructor (opts, ...streams) {  argument
21       streams.unshift(opts)
27     if (streams.length)
28       this.push(...streams)
31   [_linkStreams] (streams) {  argument
34     return streams.reduce((src, dest) => {
41   push (...streams) {  argument
42     this[_streams].push(...streams)
44       streams.unshift(this[_tail])
46     const linkRet = this[_linkStreams](streams)
50       this[_setHead](streams[0])
53   unshift (...streams) {  argument
54     this[_streams].unshift(...streams)
56       streams.push(this[_head])
58     const linkRet = this[_linkStreams](streams)
59     this[_setHead](streams[0])