Clear the selection and append aString at the end of the text widget.
Insert aString in the text widget at the current insertion point, replacing the currently selected text (if any), and leaving the text selected.
Select the whole contents of the text widget
Sets the selection of the text widget to include the characters starting with the one indexed by first (the very first character in the widget having index 1) and ending with the one just before last. If last refers to the same character as first or an earlier one, then the text widget’s selection is cleared.
Answer an empty string if the text widget has no selection, else answer the currently selected text
Answer nil if the text widget has no selection, else answer an Interval object whose first item is the index of the first character in the selection, and whose last item is the index of the character just after the last one in the selection.
Set the contents of the text widget and select them.