The visual-meta approach came about through developments for better citations in Liquid | Author. Here are my initial notes:
The information about an analog document would have to be on the same substrate level as the content in the analog world, there was no place to hide it. In digital documents however there can be a payload of information not visible to the user, in fact it is a requirement of digital documents since they need a way to convey to the operating system and reader/editor software what the document is and how it should be displayed and how it can be interacted with. This can clearly be useful, such as with the EXIF data of a photograph containing a lot of information about the technical status of the taking of the picture and has potential for adding all the citation information–and more–to a document but there are two issues: Publishers (software and companies) usually do not include this meta information and it gets stripped out on changing formats or printing.
I learnt that when Jacob implemented the ability to copy the document’s BibTeX textual citation information however, that this is findable information for a system since it starts with a unique and identifiable string, and as such, when a user copies a BibTeX from a download site to use in Author, the user does not need to copy only the the BibTeX text since if the whole web page including the BibTeX is copied, Author will easily parse the text and find the BibTeX and use it.
This gave me the most obvious revelation: Humans can read the visible text in documents and so can computer systems so why not not worry about embedding meta and instead leave it visible? This is why Author now has the option to export the BibTeX for the document at the end of the document as plain text, under the heading ‘BibTeX’. It means that Reader opens the document and ‘reads’ it and finds the BibTeX, it then uses this when the user performs a basic copy by appending it to the clipboard. When the user then pasted back into Author this is made available and on paste a dialog asks the user: Paste as plain text or use the embedded BibTeX to paste as a citation? The result is that a simple copy and paste becomes a fully formatted citation where the application accepting the paste (in this case Author) ‘knows’ that this is a citation.
The next step from this perspective is to encourage software vendors to produce PDF documents where the visual information contains semantic values, not expecting hidden information to do the job. In terms of archiving and data transfer this is useful but it’s also useful now, to make the systems more rich and robust.
Have a section at the end of the document with the BiBTeX as citation information and don’t call it meta, simply call it information but since it’s clearly marked any reader can use it in the same way as Reader / Author does.
And let’s go further. Let’s use such an appendix to describe the formatting of the document, including how headings are formatted and so on. This should allow for complete compatibility with basic PDF readers but also allow new readers to extract semantic values to allow for richer interactions, such as automatic headings interactions, citation display and interactions and so on.