support recursive ReadingOrder #359
Description
PAGE-XML's UnorderedGroup(Indexed) seems unsupported, as does recursion of groups (e.g. OrderedGroup in UnorderedGroup). So this is similar, but not identical to #181 – you can meaningfully have a flat segmentation with two group levels, for example
- a top-level UnorderedGroup for articles and lower levels for its headings and paragraphs
- a top-level UnorderedGroup comprising an OrderedGroup for main text as well as items for marginals, page-number and catch-word
- a top-level OrderedGroup that contains UnorderedGroupIndexed for table cells
- ...
UI-wise, both JPageViewer and OcrdBrowser show how to visualise sub-groups (different colors for arrows) and UnorderedGroup ("star shape"). Editing would be a challenge, though: as in #181, the group to be edited must first be selected.
(This would be useful to create GT for reading-order training for partial order relations...)