getWriteable(context, path) {
    if (!this[OBJECT_ID]) {
      throw new RangeError('getWriteable() requires the objectId to be set')
    }

    const instance = instantiateText(this[OBJECT_ID], this.elems)
    instance.context = context
    instance.path = path
    return instance
  }
Returns a writeable instance of this object. This instance is returned when
the text object is accessed within a change callback. `context` is the
proxy context that keeps track of the mutations.