How to read the syntax diagrams The -+4 symbol indicates the end of a syntax diagram Syntax fragments start with the h symbol and end with the symbol Required items appear on the horizontal line(the main path) p一 required item- Optional items appear below the main path 一 required it If an optional item appears above the main path, that item has no effect on execution, and is used only for readability optional it p一 required it If you can choose from two or more items, they appear in a stack If you must choose one of the items, one item of the stack appears on the main pati rEquired it required choiceI- If choosing one of the items is optional, the entire stack appears below the main path If one of the items is the default, it will appear above the main path, and the remaining choices will be shown below p一 required it IXThe ──
symbol indicates the end of a syntax diagram. Syntax fragments start with the ├─── symbol and end with the ───┤ symbol. Required items appear on the horizontal line (the main path).

required_item
Optional items appear below the main path.

required_item optional_item
If an optional item appears above the main path, that item has no effect on execution, and is used only for readability.

required_item optional_item
If you can choose from two or more items, they appear in a stack. If you must choose one of the items, one item of the stack appears on the main path.

required_item required_choice1 required_choice2
If choosing one of the items is optional, the entire stack appears below the main path.

required_item optional_choice1 optional_choice2
If one of the items is the default, it will appear above the main path, and the remaining choices will be shown below.

required_item default_choice optional_choice optional_choice
How to read the syntax diagrams About this book ix