**Thinking**: At the beginning of PHP learning, our code first appeared in the HTML mixed state, and then slowly became independent. Later, the PHP code was separated into different scripts, loading and calling each other. What exactly is the logic in this? **Introduction**: In fact, from the perspective of realizing business functions, any mode is acceptable. However, project development often involves team collaboration, which requires teamwork and the maintainability of later code. This leads to the practice of classifying code and dividing it into files. We have different positions for code development, and each method has its unique advantages and disadvantages.
