Introduction
Follow-Up
After redeploying the website yesterday, I noticed a wide gap between the top of the webpage and the browser's border. Initially, I thought it was a CSS issue, but upon opening the console, I discovered that the <body> tag had an unexpected  character, and the contents of the <head> had been moved inside the <body>.
The anomaly
After searching on Baidu, I found out that this was because I had used Windows Notepad to edit the PHP files in a rush. Notepad saves files with UTF-8 encoding that includes a BOM (UTF-8 with BOM). This BOM header gets placed at the beginning of the PHP file, and PHP treats any characters outside of <?php ?> as output, resulting in the extra  on the page. Additionally, UTF-8 with BOM can cause the contents of the <head> to be parsed inside the <body>.
To remove the , simply save the file again with UTF-8 encoding without BOM (UTF-8 without BOM).
Adhering to the principle of self-resolution, problems with PHP should be solved by PHP itself. I found this
It contains a PHP script that can automatically remove the BOM header from all files when placed in the root directory and accessed. However, if there are many files, the execution time can be quite long, so I added a file type check to only remove the BOM from PHP files. Here is the updated code.
How to avoid this? Don't use the lousy Notepad to edit PHP files, or you'll end up spending a whole night like I did o(TヘTo)