Conventions of syntax expressions

The syntax rules of Fortran are expressed with the following conventions, which use conventions in Fortran 2023 interpretation document for reference.

• Characters are interpreted literally as shown, except where otherwise noted.

• Letters and words enclosed between two grave accents (`) represent general syntactic classes for which particular syntactic entities must be substituted in actual statements.

• := introduces a syntactic class definition.

• || introduces a syntactic class alternative.

• { } encloses an optional item.

• { }... encloses an optionally repeated item which may occur zero or more times.

• `xyz-list` := `xyz`{, `xyz`}....

• ...... stands for a part which I do not want to discuss for the moment.