Syntax diagram conventions
A syntax diagram uses symbols to represent the elements of a command and to specify the rules for using these elements.
Syntax diagrams use position to indicate required, optional, and default values for keywords, variables, and operands.
A keyword represents the name of a command, flag, parameter, or argument. Required keywords indicate the parameters or arguments that must be specified for the command.
To read syntax diagrams, follow the path of the line. Read the diagrams from left-to-right, top-to-bottom, following the main path line.
Main path line
The main path line begins on the left with double arrowheads (>>) and ends on the right with two arrowheads facing each other (><). If a diagram is longer than one line, each line to be continued ends with a single arrowhead (>) and the next line begins with a single arrowhead. The -->< symbol indicates the end of the syntax diagram.
Required keywords
Required keywords appear on the main path line. Mutually exclusive required keywords are stacked vertically. In the following example, you must choose A, B, and C.
Optional keywords
Optional keywords indicate parameters or arguments that you might choose to specify for the command. Optional keywords appear below the main path line. Mutually exclusive optional keywords are stacked vertically. In the following example, you must choose A, B, or C.
When an optional item appears above the main line, the item above the line is the default value when no optional item is specified in the command. In the following example, the user has the same choices as above (A, B, C, or nothing at all), but if nothing is selected, the default value will be A.
Repeatable items
A stack of items followed by an arrow returning to the left means that you can select more than one item or, in some cases, repeat a single item. For example:
An arrow returning to the left means you can repeat the item.
If one or more characters appear in the arrow's line, those characters are required as a delimiter to separate repeated items.
If you can choose from two or more items, they are displayed vertically in a stack. A stack of items followed by an arrow returning to the left means that you can select more than one item or, in some cases, repeat a single item. In the following example, you can choose any combination of A, B, or C.
Variables