Why emacs touches read-only file?

[Daniel]

Hi all,

1. Create a file with permission of 444 (read-only) file.
2. Open the file using emacs.

Question.

My emacs open the read-only file as writable buffer. Also, I can
modify it and save it. (AMAZING, emacs IGNORES unix file system. WOW.)

What happened to the emacs, and how it works properly (open files as
read-only if it is read-only, and as writable if it is writable.)

Thank you,

Dan.