The so-called "oblique stroke" and "horizontal stroke" are mainly aimed at the horizontal stroke in the font. The horizontal strokes of regular script tend to tilt slightly upward, and the tilt is more obvious, which can be described as "oblique strokes"; The relative level can be described as "flat". The so-called "tight knot" and "wide knot" are mainly aimed at the inward or outward extension of the folding pen and the vertical pen. Fold the pen vertically inward, and the words are close, so it is called "tight knot"; Folding pen and vertical pen extend outward, and the characters are wider, so the oblique tight knot and flat wide knot called "wide knot" are indeed two important types of regular script knots, but this difference may not have originated in the Northern and Southern Dynasties. Zhong You's lower case "The Mark of Commendation" is a typical example of flat and wide knot, and Wang Xianzhi's "Thirteen Lines of Luo Shen Fu" is a typical example of oblique tight knot.
Mr. Sha Menghai once proposed two types: "oblique tight knot" and "horizontal wide knot".
Oblique writing is represented by Zhang Menglong's tablet in the Northern Wei Dynasty and Ou Yangxun's regular script.