[請益] that子句之前為何可以加上逗號?

[tucson (tucson)]

from :
http://www.oxfordlearnersdictionaries.com/definition/english/jigsaw?q=jigsaw

OAKD: jigsaw
(also jigsaw puzzle) (also puzzle especially in North American English)
a picture printed on cardboard or wood, that has been cut up into a lot of
small pieces of different shapes that you have to fit together again

請問非限定用法中的that子句前面不是不能加上逗號的嗎?
那為何英文解釋中的that子句 前面有加上逗號?

謝謝


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推 vincentman: that...像是插入句補充說明前述，that指的是picture
→ scju: 辭典裡這種用法超多的，我也好奇為什麼可以加逗點？
推 hsheng: http://alt-usage-english.org/excerpts/fxthatvs.html
→ hsheng: http://www.ldoceonline.com/dictionary/jigsaw
→ hsheng: http://www.dictionary.com/browse/jigsaw-puzzle
→ hsheng: 上述兩字典就沒逗點囉，參考一下
→ kaifrankwind: 全句太長或許可斟酌加一下以調整節奏
推 vincentman: 朗文字典解釋中的that是關代當fit受詞，跟牛津字典解
→ vincentman: 釋中第二個that是一樣的用法，無法對比