2.5.4 HELP Command
  The HELP command lets you display the contents of the
  VAX BASIC HELP library. A list of commands and language
  topics for which there is help available is displayed. You are
  prompted to name a command or topic with the following
  prompt:
  Topic?

  To obtain help on the environment commands, enter
  COMMANDS at the Topic? prompt. A list of commands
  is displayed on your terminal followed by the prompt
  COMMANDS Subtopic?. When you type a command name
  in response to this prompt, the HELP facility displays the
  following:

  .
        An explanation of the command's purpose
  .
        An example of its use
  .
        A list of any further subtopics available

  You can also display help text for VAX BASIC errors. The
  help texts for the BASIC error messages are grouped under
  two categories: compile-time errors and run-time errors.
  A run-time error refers to any error that occurs dur-
  ing program execution. All other errors are referred to as
  compile-time errors. Entering HELP RUN displays a list of
  the 3- to 9-character error mnemonics for the BASIC list of
  run-time errors, and entering HELP COMPILE displays a
  list of the 3- to 9-character compile-time error mnemonics.

  For example, if your program invokes a user-defined DEF
  function with a null argument, this causes VAX BASIC to
  signal the error message actual argument must be specified.
  The actual error message is as follows:
  %BASIC-E-ACTARGMUS, actual argument must be specified

  You display the help text by entering the following command:
  HELP COMPILE ACTARGMUS

  The following text displays on your screen:
  ACTARGMUS
          ERROR - A DEF function reference contains a null argument, for
          example FNA(1,,2). Specify all arguments when referencing a DEF
          function.

  You can access run-time errors with either the mnemonic
  or the error number. You specify the error number with the
  letters ``ERR'' followed by the error number. For example,
  you can display the HELP text for the end-of-file error by
  using the mnemonic as follows:
  HELP RUN ENDFILDEV

  If you know only the error number, enter the following:
  HELP RUN ERR11

  VAX BASIC displays the appropriate mnemonic for that
  error.