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    variables have been replaced by warning identifiers that are used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.  Now,
    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


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