works in tight cooperation with the instance passsed as the
variable argument (e.g., a pdk.Variables.IntVariable or
a pdk.Variables.FloatVariable instance).
The .Clone and the .Validate methods are used by the
wxWindows framework; the TransferDataToWindow /
TransferDataFromWindow methods supposedly are, too.
Note that because wxWindows creates more than one validator
for each widget being validated (for reasons that escape my
understanding), we have to store the last "good" (validated)
value for each widget separately (see the
_LastGoodValueRegistry class).
ensures that we have a valid value in the widget when the user is done
editing (i.e., leaves the window with the mouse). Posts a TEXT_ENTER
event to notify the associated widget.
Note that a similar hook with EVT_KILL_FOCUS does cause wxPython to
crash when the parent window is destroyed while the validated widget
has the focus.