code: function nodeInjectmd (opts) {
    const inBuf = bl()
  
    assert.equal(typeof opts, 'object', 'opts should be an object')
    assert.equal(typeof opts.in, 'string', 'opts.in should be a string')
    assert.equal(typeof opts.tag, 'string', 'opts.tag should be a string')
  
    const inFile = opts.in
    const tag = opts.tag
    const startTag = new RegExp('<!--\\s*START ' + tag + '\\s*-->')
    const endTag = new RegExp('<!--\\s*END ' + tag + '\\s*-->')
  
    assert.equal(typeof opts, 'object', 'opts must be an object')
  
    const rs = new stream.PassThrough()
  
    rs.pipe(inBuf)
  
    rs.on('end', function () {
      var tagMode = false
      const mdPath = path.join(process.cwd(), inFile)
      const irs = fs.createReadStream(mdPath)
      const its = split(parse)
      const tmpBuf = bl()
  
      irs.pipe(its).pipe(tmpBuf)
  
      tmpBuf.on('finish', function () {
        const ws = fs.createWriteStream(inFile, { flags: 'w' })
        const rs = tmpBuf.duplicate()
        rs.pipe(ws)
      })
  
      function parse (line) {
        if (startTag.test(line.trim())) {
          tagMode = true
          const res = line + EOL + String(inBuf) + EOL
          return res
        } else if (endTag.test(line.trim())) {
          tagMode = false
          return line + EOL
        } else if (!tagMode) {
          return line + EOL
        }
      }
    })
  
    return rs
  }
docs: Inject markdown into markdown obj -> null