code: func (t *Text) SetStyleAt(pos int, style tcell.Style) {
  	if pos < 0 || pos >= len(t.text) || t.widths[pos] < 1 {
  		return
  	}
  	t.styles[pos] = style
  	t.PostEventWidgetContent(t)
  }
docs: // SetStyleAt sets the style at the given rune index.  Note that for
  // strings containing combining characters, it is not possible to
  // change the style at the position of the combining character, but
  // those positions *do* count for calculating the index.  A lot of
  // complexity can be avoided by avoiding the use of combining characters.