The StyledText widget implements this listener to receive
notifications when changes to the model occur.
It is not intended to be implemented by clients or by
implementors of StyledTextContent.
Clients should listen to the ModifyEvent or ExtendedModifyEvent
that is sent by the StyledText widget to receive text change
Implementors of StyledTextContent should call the textChanging
and textChanged methods when text changes occur as described
below. If the entire text is replaced the textSet method
should be called instead.
This method is called when the content is about to be changed.
Callers also need to call the textChanged method after the
content change has been applied. The widget only updates the
screen properly when it receives both events.
event - the text changing event. All event fields need
to be set by the sender.
This method is called when the content has changed.
Callers need to have called the textChanging method prior to
applying the content change and calling this method. The widget
only updates the screen properly when it receives both events.