I want to develop a PHP web application. the bottom layer does not know where to start. I hope you can give me some advice.

I want to develop a PHP web application. I don't know where to start from the bottom layer. I hope you can give me some advice on developing a PHP web application. I don't want to use the framework. I want to write it from the bottom layer, improve your programming skills, but you don't know where to start. I have seen many open-source programs before, most of which are to write an entry file "index. php "and then introduce other users who want to develop a PHP web application. the bottom layer does not know where to start. I hope you can give me some advice.
If you want to develop a PHP web application and do not want to use the framework, you want to write it from the underlying layer to improve your programming level, but you don't know where to start. I have seen many open-source programs before, most of which are to write an entry file "index. "php" and then introduce other files, but I don't know how to write it when I write it myself. I hope you can give me some comments. thank you!

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Require an initialization file
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Then you should stop writing. PHP will write pages. if it cannot be written, it won't.

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Discussion

Reference:

Then you should stop writing. PHP will write pages. if it cannot be written, it won't.

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I want to write down an underlying architecture. when others understand this architecture, they will be able to add their own functions to this architecture.

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... Terms are not quite good...