Who can explain this download?

Who can explain this download if (is_file ($ file )){
Header ("Content-Type: application/force-download ");
Header ("Content-Disposition: attachment; filename =". basename ($ file ));
Readfile ($ file );
Exit;
} Else {
Echo "the file does not exist! ";
Exit;
}


What is application/force-download?
Content-Disposition: What is attachment? what is filename and readfile?

Reply to discussion (solution)

Application/force-download is a mime type used to inform the recipient that this is an object download.

Content-disposition is an extension of the mime protocol.
Content-Disposition: attachment informs the receiver that the filename attribute following is the reference file name.
A download dialog box is usually displayed in the browser and the file name is displayed.

Readfile is a php function.
It can be seen from the function name that its function reads (read) files)