A command starts at the beginning of a line and extends to the next Return. (Usually a command fits on one line, but sometimes it goes over.) The first word is the name of the command. It may be followed by words that give more detailed information
(modifiers, parameters, or arguments).
The visual command uses the word "effect" simply to read better—"zoom open" is the actual visual effect that will happen (during the next go command). See the visual command.* See also the list of effects.*