Currently [1] ATK has the following AtkTextBoundary variants:
  ATK_TEXT_BOUNDARY_CHAR
  ATK_TEXT_BOUNDARY_WORD_START
  ATK_TEXT_BOUNDARY_WORD_END
  ATK_TEXT_BOUNDARY_SENTENCE_START
  ATK_TEXT_BOUNDARY_SENTENCE_END
  ATK_TEXT_BOUNDARY_LINE_START
  ATK_TEXT_BOUNDARY_LINE_END

This is overkill (ATs don't need them all) and also more work for implementors of ATK.

Instead we should have:
  ATK_TEXT_BOUNDARY_CHAR
  ATK_TEXT_BOUNDARY_WORD
  ATK_TEXT_BOUNDARY_SENTENCE
  ATK_TEXT_BOUNDARY_LINE

The word, sentence, and line boundaries would have the same behavior as the "start" variant.

On a related note, Orca is the main (if not the only) consumer of this functionality. It no longer uses the END variant for the above boundaries.

[1] https://developer.gnome.org/atk/unstable/AtkText.html#AtkTextBoundary