Commodore 128 System Manual page 239

Keywords are words that are part of the BASIC language. They
are the central part of a command or statement, and they tell the
computer what kind of action to take. These words cannot be
used as variable names. A complete list of reserved words and
symbols is given in Section 20.
ARGUMENTS, also called parameters, appear in lower-case
letters. Arguments complement keywords by providing specific
information to the command or statement. For example, the
keyword LOAD tells the computer to load a program while the
argument tells the computer which specific program to load. A
second argument specifies from which drive to load the program.
Arguments include filenames, variables, line numbers, etc.
SQUARE BRACKETS [ ] show optional arguments. The user
selects any or none of the arguments listed, depending on
requirements.
ANGLE BRACKETS < > indicate the user MUST choose one of
the arguments listed.
A VERTICAL BAR | separates items in a list of arguments when
the choices are limited to those arguments listed. When the
vertical bar appears in a list enclosed in SQUARE BRACKETS,
the choices are limited to the items in the list, but the user still
has the option not to use any arguments.
ELLIPSIS ... a sequence of three dots means an option or
argument can be repeated more than once.
QUOTATION MARKS " " enclose character strings, filenames
and other expressions. When arguments are enclosed in
quotation marks, the quotation marks must be included in the
command or statement. Quotation marks are not conventions
used to describe formats; they are required parts of a command
or statement.
PARENTHESES () When arguments are enclosed in
parentheses, they must be included in the command or
statement. Parentheses are not conventions used to describe
formats; they are required parts of a command or statement.
16-5