Generate an ISSN barcode

This relates to:

https://answers.launchpad.net/inkscape/+question/290762 and is for Inkscape 0.91 [windows 8.1 64bit version]

I want to generate an ISSN Barcode which is an EAN13 barcode but it has digits 14 & 15 to denote, in my case, the month of issue of a magazine. However, the barcode generator does not let me do this. I also notice that there isn't a light margin indicator [chevron] generated. The specification for an ISSN is shown below and taken from BEST PRACTICE FOR BAR CODING AND ISSUE NUMBERING OF MAGAZINES, PARTWORKS, COLLECTABLES AND PROMOTIONAL VOUCHERS. Updated – June 2014 PRODUCED BY Professional Publishers Association and Association of Newspaper and Magazine Wholesalers [see here http://www.anmw.co.uk/anmw/documents/PPA_Barcode_Guidelines.pdf]

Magazine issue barcodes are represented in EAN 13 format with a 2-digit add-on code.

• GS1 Prefix (digits 1-3): 977 for magazines with an ISSN

• ISSN Component (digits 4-10): The first 7 digits of the 8 digits ISSN (the last digit, which is a check digit, is deleted as it is redundant when included within the EAN-13 which has its own check digit). The UK Centre at the British Library assigns the ISSN.

• Sequence Variant (digits 11-12): Used on magazines to indicate price changes. For a new magazine start with 00 and move up by 01 for each price change either up or down. Actual prices are not represented anywhere in the bar code. For “one-off” special priced issues an initial sequence variant of 99 should be used and thereafter decreasing the value to 98, 97, 96, etc.

• Check Digit (digit 13): Derived from a calculation, based on the first 12 digits, used to check that the code is correct if manually entered into a system. The Film Master Supplier or your dedicated bar code software would normally calculate the check digit. Please see GS1 UK website for an example of the check digit calculation http://www.gs1uk.org/ - then select ‘Check Digit Calculator’ from the Quick Links menu.

• Add-on (digits 14-15): The 2-digit code used to identify each issue. The section overleaf defines the guidelines for numbering different types and frequencies of magazines. The add-on changes for every issue therefore a new bar code symbol is required for each issue.

• Light Margin Indicator (chevron): This appears in the right-hand margin of the symbol. It ensures there is sufficient margin for the bar code reader to realise it has finished the bar code.

Martin Owens proposed the following answer:
I have made an Ean2 barcode for the extension and will work on allowing the cheveron and automatic addition of extension bars for EAN13.

Please stand by for resolution and consider open a bug report for the new feature.