I'm working on a way to take advantage of Ediff's fine highlighting
feature within Diff mode buffers. But calling ediff-regions-internal
programmatically with BUFFER-A the same as BUFFER-B doesn't work,
leaving only the region between BEG-B and END-B highighted. This is
because ediff-extract-diffs first resets point in both buffers (changing
point in BUFFER-A unintentionally), then builds the diff vector by
moving by lines in each buffer.
The fix is simple, and it allows ediff-regions-internal to work with
non-overlapping regions in the same buffer: Don't set point in each
buffer until necessary: