Occurs before editing operations
TRVChangingEvent = procedure (Sender: TCustomRichViewEdit;
var CanEdit: Boolean) of object;
property OnChanging: TRVChangingEvent;
Set CanEdit to False to prevent editing.
This event occurs when:
▪user tries to edit text, or
▪calling any editing-style method (before changes are actually done).
Viewer-style methods do not generate this event.