structural concordance: collect more (possible) pairs

[bertsky]

In en/trans/structurmets2page.dita, we could add the Page/@type types with their DFG Strukturdatenset counterparts (some of which are already covered in en/trans/structur_gtpageformat.dita, perhaps because they were also in the Zot format already):

• cover_back: back-cover
• cover_front: front-cover
• binding / endsheet / spine / paste_down / colour_checker: empty
• title_page: title
• table_of_contents: table-of-contents
• index: index

Also, why is mets:div/@type=table likened to pc:TextRegion/@type=heading and not @type=caption (or pc:TableRegion directly)? (Same probably goes for mets:div/@type=map vs. caption / pc:MapRegion, as well as mets:div/@type=musical_notation vs. caption or pc:MusicRegion.)

Also, where is illustration?

Next, I would have expected that pc:GraphicRegion/@type gets mapped, too:

• annotation: handwritten-annotation
• stamp: stamp
• printers-mark: decoration
• ...?

Furthermore, IIUC it seems plausible to also suggest mapping some of the mets:div types to pc:ReadingOrder types:

• text: paragraph
• illustration: figure
• article: article
• section / chapter / part: div

Generally, it would also help to strictly differentiate between structural types (what ENMAP calls contentUnit) and layout types (what ENMAP calls contentItem).

Lastly, how about also collecting concordance between mets:div types and alto:LayoutTags and alto:StructureTags? I can see many similar entities in the official documentation. Perhaps a full discussion of this would also need to include the various ENMAP profiles...