It is a format used to identify the fourth-level subtitle in a document, and is usually used to further subdivide the content under the third-level subtitle. Four-level titles are usually not used in paper directories, but mainly used in the text. They are the formats used to identify the four-level subheadings in a document, and are usually used to further subdivide the content under the three-level subheadings. Generally speaking, the font size and font size of the four-level title are the same as the text, that is, the small four characters and the song style.