The word 누나 is not in the Hangul dictionary but appeared in the Hanja dictionary. When I typed "nuna", only the Hanja 姐 appeared in the candidate list.

我注意到仓库中有一张罗马化的表音图，但是我经过搜索之后，发现该韩文罗马化方案既非常见的 GongjinCheong Romaja，也非 HNC Romaja，甚至也不是官方发布 的转写方案。
虽然个人觉得非常适合韩语学习者使用，但是一直没有找到对应的标准，所以想要来请教一下。

Observations

• Typing the key sequence "hangyl" produces "항을" instead of the expected "한글".
  A "ㅇ" is auto-inserted before "yl" to produce "을". The sequence "hangyl" is undesirably segmented into "hang" and "yl".

• Typing the key sequence "haseixio" or "haseiio" produces "핫에요" instead of the expected "하세요".
  A "ㅇ" is auto-inserted before "ei". The sequence "hasei" is undesirably segmented into "has" and "ei".

Reason

Syllable initial "ㅇ" is required in some cases to disambiguate syllable boundary in Hangul. Hence, input methods like HNC Romaja on macOS require the input of "ㅇ" to eliminate ambiguity.

Fix

Comment out the following line in hangyl.schema.yaml:

speller:
  ...
  algebra:
    # - derive/(^|[ '])x?([aeiouy])/$1$2/

Implications of the fix

"ㅇ" is always required at the syllabe initial position:

• The key sequence "an" produces "ㅏㄴ". To produce the syllable "안", type "xan" or "qan" instead.
• The key sequence "haseiio" produces "하세ㅛ". To produce the word "하세요", type "haseixio" or "haseiqio" instead.