Add Article variant to StructRole2

[dcalvo]

PDF 2.0 standard structure namespace uses Article instead of Art. Adds the missing StructRole2::Article variant so consumers can emit the preferred 2.0 name.

[saecki]

I'm not sure where you got this from. Could you name the part of the PDF 2.0 spec where this is listed?

[dcalvo]

Closing this. After verifying against ISO 32000-2:2020 (Table 365), Art was not renamed to Article in the PDF 2.0 standard structure namespace. It was removed from the 2.0 namespace entirely, along with some others. The PDF 1.7 namespace (which remains the default in PDF 2.0 files) still defines Art, so consumers should continue using that.

For context on why this came up: I encountered a corpus of PDFs claiming PDF/UA-2 compliance that used /Article as a structure type. It turns out these PDFs are actually non-conforming as /Article isn't a valid tag in either standard namespace. I guess the upstream authoring tool has a bug or failed to generate a role map entry.

Apologies for the noise!