Determines the starting position of a text selection, or -1 if the TextBox has no range of selected text. If the value is -1 or equivalent to
TextBox/CursorPosition|CursorPosition, there is no range of text selected. This property uses the same positioning logic as CursorPosition. SelectionStart will be greater than CursorPosition if the cursor is at the beginning of a selection, and less than CursorPosition if the cursor is at the end.
This code sample demonstrates reading the current selection of a