Tk automatically creates class bindings for entries that give them
the following default behavior:
Clicking mouse button 1 in an entry positions the insertion cursor
just before the character underneath the mouse cursor and sets the
input focus to this widget.
Dragging with mouse button 1 strokes out a selection between
the insertion cursor and the character under the mouse.
The ends of the selection can be adjusted by dragging with mouse
button 1 while the shift key is down; this will adjust the end
of the selection that was nearest to the mouse cursor when button
1 was pressed.
The view in the entry can be adjusted by dragging with mouse button 2.
If the input focus is in an entry widget and characters are typed on the
keyboard, the characters are inserted just before the insertion cursor.
Control-h and the Backspace and Delete keys erase the character just
before the insertion cursor.
Control-w erases the word just before the insertion cursor.
Control-u clears the entry to an empty string.
Control-v inserts the current selection just before the insertion cursor.
Control-d deletes the selected characters; an error occurs if the selection
is not in this widget.
If the entry is disabled using the state option, then the entry's
view can still be adjusted and text in the entry can still be selected,
but no insertion cursor will be displayed and no text modifications will
The behavior of entries can be changed by defining new bindings for
individual widgets or by redefining the class bindings.