5.8 Keywords and Reserved Words
  Keywords are elements of the BASIC language. Keywords
  that are not reserved can be used as user identifiers such
  as labels, variable or constant names, or names of MAP or
  COMMON areas. Depending upon the location of the key-
  word in your program statement, the compiler will treat it
  as either a keyword or a user identifier. Your programs use
  keywords and reserved words to:

  .
        Define data
  .
        Perform operations
  .
        Invoke functions

  See the DEC BASIC and VAX BASIC for OpenVMS Systems
  Reference Manual for a list of keywords and reserved words.

  Keywords determine whether the statement is executable
  or nonexecutable. Executable statements such as PRINT,
  GOTO, and READ perform operations. Nonexecutable state-
  ments such as DATA, DECLARE, and REM describe the
  characteristics and arrangement of data, usage information,
  and comments.

  Every statement except LET must begin with a keyword. A
  keyword cannot have embedded spaces or be split across lines
  of text. There must be a space or tab between the keyword
  and any other variables or operators.

  There are also phrases of keywords. In this case, the spacing
  requirements vary.