I was trying to understand this sentence:

それは聞いたことのない少女の声であった。

And I found [this
answer](https://japanese.stackexchange.com/questions/69368/what-does-
verb%e3%81%93%e3%81%a8%e3%81%ae%e3%81%82%e3%82%8bnoun-mean).

The answerer changed ことのある to ことがある, stating that "の is used as a subject
marker in some cases."

Does this mean I can treat ことのある and ことがある as roughly the same? (の and が are
being used to identify a subject)?
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2021-07-29T21:44:29.730
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2021-07-29T21:44:29.730
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question
grammar meaning
Is ことのある the same as ことがある?