> Text model based on sequence of span objects. There are now two kind of spans: CharacterSpan and LineSeparator. Each span has reference to next and previous spans. There is TxSelection object which contains cursor. So you can insert new text at cursor, you can cut selection, replace selection with another text. Such maniulation changes text model structure. It can create new span objects. It can split current span at cursor position, It can remove selected spans. Also you can move cursor up, down, left, right. Cursor always know about current span and span position.

If this is not in the class comments can you add it?