One or two meanings:
(1) Annotate and explain the sentence.
(2) the sentence content of the notes.
Secondly, annotations are used for three reasons:
1, explain the text in words.
For example, The Scholars in the Later Han Dynasty and Yang Lun: "Fu Dufeng's Biography of Ancient Literary History, with Jia Kui in Lintong County as the training, Ma Rong as the biography and Zheng Xuan as the annotation, makes the history of ancient literature famous all over the world."
2. General explanation.
For example, The Legend of Heroes of Children dates back to Chapter 38: "If it is good, his sister will be more and more embarrassed to be commented by this young lady."
3. Explain the words.
For example, Lu Wu Ji of the Three Kingdoms, "Selected Books": "After a few years of intensive reading, I was roughly aware of it at the age of half, so I created a note and failed."