One of "needed", "always" or "never". If "needed", a new window is opened to inspect the movements only if the movements table is too big to be displayed in R's console. If "always", a graphical interface is always created when the possibility to invalidate events emerges. If "never", a graphical interface is never invoked. In this case, if the table to be displayed does not fit in R's console, a temporary file will be saved and the user will be prompted to open and examine that file. Defaults to "needed".