A TextFlow instance dispatches this event after a compose operation completes.
Each text container has two states: composition and display. This event notifies
you when the composition phase has ended. This provides an opportunity to make any
necessary and appropriate changes to the container before you display the text.
For example, you can use this event to add highlighting of certain words or
characters in the text flow before the text is displayed.
The three main methods that dispatch this event are compose(),
updateToController(), and updateAllControllers().
All three of these methods are in the StandardFlowComposer class.
Note: If the event is dispatched by the
updateAllControllers() method, do not call
updateAllControllers() again in your event handler function.
Such a call would be a recursive call because the updateAllControllers()
method executes both the composition and display steps. The updateAllControllers()
dispatches this event after composition completes, but before the display step executes.
The same reasoning applies to the updateToController() method.