Summary of changes for version 3.0:
----------------------------------

  * Previous versions of Octave had a number of built-in variables to
    control warnings (for example, warn_divide_by_zero).  These
    variables have been replaced by warning identifiers that are used
    with the warning function to control the state of warnings.

    For example, instead of writing

      warn_divide_by_zero = false;

    to disable divide-by-zero warnings, you should write

      warning ("off", "Octave:divide-by-zero");

    You may use the same technique in your own code to control
    warnings.  For example, you can use

      warning ("My-package:phase-of-the-moon",
               "the phase of the moon could cause trouble today");

    to allow users to control this warning using the
    "My-package:phase-of-the-moon" warning identifier.

    You may also enable or disable all warnings, or turn them into
    errors:

      warning ("on", "all");
      warning ("off", "all");
      warning ("error", "Octave:divide-by-zero");
      warning ("error", "all");

    You can query the state of current warnings using

      warning ("query", ID)
      warning ("query")

    (only those warning IDs which have been explicitly set are
    returned).

    A partial list and description of warning identifiers is available
    using

      help warning_ids


  * All built-in variables have been converted to functions.  This
    change simplifies the interpreter and allows a consistent
    interface to internal variables for user-defined packages and the
    core functions distributed with Octave.  In most cases, code that
    simply accesses internal variables does not need to change.  Code
    that sets internal variables will change.  For example, instead of
    writing

      PS1 = ">> ";

    you will need to write

      PS1 (">> ");

    If you need write code that will run in both old and new versions
    of Octave, you can use something like

      if (exist ("OCTAVE_VERSION") == 5)
        ## New:
        PS1 (">> ");
      else
        ## Old:
        PS1 = ">> ";
      endif


See NEWS.2 for old news.