What is the content and significance of Zhang Zhongjing's theoretical principles of four diagnosis and eight principles of syndrome differentiation and treatment?

Through a long medical career and careful research, Zhang Zhongjing has been able to distinguish whether a patient's symptoms are yin or yang according to the four diagnoses. The disease is on the surface, or has gone deep into the viscera; Insufficient or surplus; It's cold or hot. Yin and yang, exterior and interior, deficiency and excess, cold and heat are called eight categories of TCM diagnosis. The theoretical principle of syndrome differentiation and treatment based on four diagnoses and eight outlines is the core idea of traditional Chinese medicine. Zhang Zhongjing has made great contributions to the establishment of this theoretical principle.