One of the more recent "sub-standards" of PDF to emerge from ISO is PDF/UA, which is also known as ISO-14289. The "UA" here stands for Universal Accessibility, and like PDF/A, PDF/X, PDF/E etc., PDF/UA imposes a particular set of rules on how the PDF is created: in this case, rules intended to make reading a PDF easier for those using assistive technology, such as screen readers for the partially sighted.
The three releases of PDF/A to date have all specified a conformance level, and up until now our API has only supported conformance level "B". Conformance level "A" is stricter, and requires the PDF content to be tagged, to provide some structure to the content of the PDF. This is what PDF/A-1a, PDF/A-2a and PDF/A-3a have in common with PDF/UA, and why our 2.20 release adds support both creating and validating PDF/A-1a, PDF/A-2a and PDF/A-3a documents.
The most conspicuous requirement is for the PDF to be "Tagged" with structural content. This interleaves an XML-like tag hierarchy into the document content, assigning text and graphics to familiar elements like Paragraphs and Articles. This must be done while the PDF is being created: although it's possible to add these tags to the document after creation with tools like Acrobat, it's is not something we'd expect to be done programmatically as it requires visual analysis of the document.
With our API, adding these tags is done with the beginTag and endTag methods on the PDFPage, PDFCanvas and LayoutBox classes, to inject the XML-like tag structure into the PDF content while it's being created.
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