=over 4

=item new($issn)

The constructor accepts a scalar representing the ISSN.

The string representing the ISSN may contain characters
other than [0-9xX], although these will be removed in the
internal representation.  The resulting string must look
like an ISSN - the first seven characters must be digits and
the eighth character must be a digit, 'x', or 'X'.

The string passed as the ISSN need not be a valid ISSN as
long as it superficially looks like one.  This allows one to
use the `fix_checksum' method.

One should check the validity of the ISSN with `is_valid()'
rather than relying on the return value of the constructor.

If all one wants to do is check the validity of an ISSN,
one can skip the object-oriented  interface and use the
c<is_valid_checksum()> function which is exportable on demand.

If the constructor decides it can't create an object, it
returns undef.  It may do this if the string passed as the
ISSN can't be munged to the internal format.

=item $obj->checksum

Return the ISSN checksum.

=item $obj->as_string

Return the ISSN as a string.

A terminating 'x' is changed to 'X'.

=item  $obj->is_valid

Returns 1 if the checksum is valid.

Returns 0 if the ISSN does not pass the checksum test.
The constructor accepts invalid ISSN's so that
they might be fixed with `fix_checksum'.

=item  $obj->fix_checksum

Replace the eighth character with the checksum the
corresponds to the previous seven digits.  This does not
guarantee that the ISSN corresponds to the product one
thinks it does, or that the ISSN corresponds to any product
at all.  It only produces a string that passes the checksum
routine.  If the ISSN passed to the constructor was invalid,
the error might have been in any of the other nine positions.

=back

• Igor Vlasenko
• Kirill Maslinsky

• perl-Business-ISSN