The following information will help you to understand the
structure of syntax diagrams.
- Read the syntax diagrams from left to right, from top to bottom,
following the path of the line. The following conventions are used:
- The >>--- symbol indicates the beginning of a
syntax diagram.
- The ---> symbol indicates that the syntax diagram
is continued on the next line.
- The >--- symbol indicates that a syntax diagram
is continued from the previous line.
- The --->< symbol indicates the end of a syntax
diagram.
- Required items appear on the horizontal line (the main path).

>>-required_item-----------------------------------------------><
- Optional items appear below the main path.

>>-required_item--+---------------+----------------------------><
'-optional_item-'
- If you can choose from two or more items, they appear vertically,
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 appears
above the main path, and the remaining choices are shown below.

.-default_choice---.
>>-required_item--+------------------+-------------------------><
+-optional_choice1-+
'-optional_choice2-'
- An arrow returning to the left, above the main line, indicates
an item that can be repeated.

.-----------------.
V |
>>-required_item----repeatable_item-+--------------------------><
If the repeat arrow contains a comma, you must
separate repeated items with a comma.

.-,---------------.
V |
>>-required_item----repeatable_item-+--------------------------><
- Sometimes a diagram must be split into fragments. The syntax fragment
is shown in the list of descriptions of the options, but the contents
of the fragment should be read as if they are on the main path of
the diagram. For example, the description of the fragment |
Trace-options | appears under Trace options in the
list of the descriptions of the options of the command.
- Variables appear in all lowercase italic letters (for example, column-name).
They represent user-supplied names or values.
- Separate keywords and parameters by at least one space if no intervening
punctuation is shown in the diagram.
- Enter punctuation marks, parentheses, arithmetic operators, and
other symbols, exactly as shown in the diagram.
- Footnotes are shown by a number in parentheses, for example (1).