code: func (c *Cursor) Update(newinput string) {
  	a := c.input
  	b := []rune(newinput)
  	i := c.Position
  	a = append(a[:i], append(b, a[i:]...)...)
  	c.input = a
  	c.Move(len(b))
  }
docs: // Update inserts newinput into the input []rune in the appropriate place.
  // The cursor is moved to the end of the inputed sequence.