For some strange questions about PHP and include, please advise.

For some strange questions about PHP and include, find out require_once '.../../system/common. php ';
The page header may be inexplicably added with a garbled string.
It is useless to call, but the echo content is not found in common. php.
Later, I accidentally changed the common. php file name to common1.php.
Require_once '.../../system/common1.php ';
The name is changed back to common. php. What's going on? although common1.php can be used temporarily now, I have to think about it, and ask my predecessors for help.

Reply to discussion (solution)

Search the bom header

Search the bom header

I learned this question. thank you very much for solving it.