Ex has five distinct modes. The primary mode is command mode. Commands are entered in command mode when a `:' prompt is present, and are executed each time a complete line is sent. In text input mode ex gathers input lines and places them in the file. The append, insert, and change commands use text input mode. No prompt is printed when you are in text input mode. This mode is left by typing a `.' alone at the beginning of a line, and command mode resumes.
The last three modes are open and visual modes, entered by the commands of the same name, and, within open and visual modes text insertion mode. Open and visual modes allow local editing operations to be performed on the text in the file. The open command displays one line at a time on any terminal while visual works on CRT terminals with random positioning cursors, using the screen as a (single) window for file editing changes. These modes are described (only) in An Introduction to Display Editing with Vi.