Reading syntax diagrams

• The keywords appear in all uppercase letters.
• The values associated with the keywords are either default values, non-variable values, or variable values. Default values are shown by underlined, upper-case letters. Non-variable values are shown by upper-case letters and variable values by lower-case letters.
• Required keywords are on the main line.
• Optional keywords are below the main line.
• If there is a vertical list of keywords or values to choose from and one of the choices lies on the main path, a keyword or value in the list is required. If all choices lie below the main path, a keyword or value is optional.
• A recursive arrow above a stack indicates that you can specify multiple keywords and values or you can repeat keywords and values.
  • If one item is on the main path, you can specify as many keywords or values as you want, but you must specify at least one.
  • If none lie on the main path, you can specify as many as you want, but none are required.
  • If a comma lies on the recursive arrow, you must separate the keywords or values with commas.

The following figure provides examples of syntax diagrams and what they mean.