In section 3.1.5, there is a note with translation issues, making it impossible to understand.

"The pattern shown in ③ was first invented in books such as novels, which use frequent line feeds and corner brackets in dialogues, for which the first line indent with one em spacing or one and a half em spacing (then this pattern was accepted and adopted by general books)."
"③の方法は，小説などで会話が多い場合，改行行頭の括弧の字下げを全角アキ又は全角半（全角の1.5倍）アキとすると下がり過ぎになることから考えられた方法である（これが一般書にも採用されるようになっている）．"

The portion "と下がり過ぎになることから考えられた" is missing in the translation, making the sentence meaningless by removing the reason the sentence was trying to state.

A potential translation accounting for the missing part could be as follows:
'The pattern shown in ③ was first invented in books such as novels, which use frequent line feeds and corner brackets in dialogues, for which the first line indent with one em spacing or one and a half em spacing was considered to be too much (then this pattern was accepted and adopted by general books).'