delete-text
This signal is emitted when the delete_text() method is called, which happens internally when the user presses the delete button and text is currently selected.
The data that is passed with this signal consists of the calling class and the start and end positions of the selection.
Callback function
void callback(GtkEditable widget, int start_pos, int end_pos);
忘却曲線を使ってこの知識を確実に記憶に残す
