Feedback from Alex Chiculita, Adobe:
We have Region.getRegionFlowRanges that returns the Range array while there is no way to get all the regions of a specific range. For example, there's no NamedFlow.getRegionsByFragmentRange(). There's only NamedFlow.getRegionsByContentNode() . I'm not sure if it's needed, but it feels like it should go both ways.
use case proposed by Alex:
Could be used for detecting what regions are affected by the user selection. For example: the user selects some text and you might need to highlight the selected regions or show a contextual menu near the regions.
Added as a possible future feature: