docs: function listen () {
      if (typeof obs === 'function') {
        releases.push(obs(binder.onUpdate))
      }
      rebindAll()
  
      Array.from(itemInvalidators.values()).forEach(function (invalidators) {
        invalidators.forEach(function (invalidator) {
          invalidator.release = invalidator.observable(invalidate.bind(null, invalidator))
        })
      })
  
      if (opts && opts.onListen) {
        var release = opts.onListen()
        if (typeof release === 'function') {
          releases.push(release)
        }
      }
    }