What is the meaning of "outline" in the outline?

"Take an outline and open your eyes, and solve a volume to make it clear to everyone." As soon as the main rope on the fishing net is lifted, the net will be completely opened, and the contents of one roll will be explained clearly, and the meaning of the rest of the article will be understood. To give an outline and solve a paper is to grasp the main contradiction. ?

From: Zheng Xuan's Preface to the History of Han Poetry: "Read the outline, solve a volume and make it clear." ?

Introduction to Preface to Poetry;

According to the dictionary, the class is the main rope on the fishing net, and the eye is the eye on the net. If you leave the main rope of the fishing net, all the meshes will open. By extension, the outline is the general outline of things, aiming at subordinate departments. If we grasp the general part, that is, the principal contradiction, the problem will be easily solved. The metaphor of doing work and doing things solves the key of things and also drives to solve other links.